Part 3; Please read parts 1 and 2 first

In our day the Morse code is still used only from the only used by radio amateurs or OM acronym of "Old Man" who are known by the initials O.M (Old Man) , but experts in war and sci-fi think that one day in the future if our technology will missing is lost, the  Morse code will be reborn because it is the more simply a simple way to communicate.

I think a pale blue background may be easier to read than green, so I'll change styles...

1/ As noted in Part 2, this is better off as a separate sentence.

2/ Using "the Morse code" is not really wrong but is not common in English. It is usually just referred to as "Morse code".

3/ I would remove the word "still". Yes, it is "still used" but you would normally use that word if you wanted to emphasise that something was still common, perhaps even flourishing. In this case it isn't; your main point is that it is only used by a few people.

4/ In English you only capitalise proper nouns; the names of specific people, places, etc. You wouldn't capitalise "radio amateurs", which is just a description of a group of people.

5/ I changed the structure of the sentence a little. The use of or suggested that there are two groups of people; radio operators and "Old Men". Instead "O.M. is just another name for this particular group of radio operators who can still use Morse code.

6/ As per the notes in Part 2, O.M. is not an acronym, it's an initialism. However in this case "initials" probably works better.

7/ "Will missing" is missing a verb; specifically the verb "to be" (essere). You could say "will be missing" - though not in this sentence. You could say "is missing" instead. However I wouldn't say that either because it conveys the wrong idea. It suggests that we have just misplaced our technology and can't find it. Instead you are talking abut a situation where it is lost, perhaps as a result of a war.

8/ Again "simply" is an adverb; you would use it to modify a verb. In this case you want an adjective to describe the way to communicate. Also "more" would be used as a comparative; it is "more simple" compared to what? I therefore got rid of the "more" and just said "a simple way".

S.O.S

This sound allowed of save life to save the life of many sailormen in the past. In our day Nowadays the morse code is still used only from the Radio Amateurs or OM acronym of "Old Man" by radio amateurs to spell initialisms, like OM for "old man", but experts in war and sci-fi think that one day in the future, if our technology will went missing, the morse code will be reborn because it is the more simply it's the most simple way to communicate.

Notes:
Always remember that interrogative and negative sentences in English are built using "to do" as the auxiliary verb. Also check that all sentences have an "explicit" subject to avoid writing just "is" when it should be "it's".

I would rewrite the second paragraph, because the wording sounds a bit unnatural. 

Part 2; please read part 1 first.

The sound in Morse code of SOS is very simply simple to remember because is composed from three short tones, three long tones and three short tones; his Its graphical rappresentation representation is: ...---... (three dots, three lines dashes, three dots).

1/ See my earlier note about capitalising Morse.

2/ Simply is an adverb; it modifies a verb. In this case you want an adjective; something that describes the noun "The sound". That's "simple" rather than "simply".

3/ I've left "from" alone because it's not technically wrong (here), but in English it is more common to use "of" after the word "composed".

4/ Since there is more than one tone in each case, that word needs to be plural; "tones", not "tone".

5/ In English "His" normally only refers to people or other living beings which have a male sex (men, stallions, bulls, etc), not inanimate objects or abstract concepts like Morse code. Those normally use "it" rather than "him". There are a few exceptions to this. Ships, for example, are often referred to as "her" (although "him" was used in the cold war days to refer to Warsaw Pact ships"), and sometimes cars will be referred to as "her" as well. However that's an idiom, not a correct use of the word. Also I would suggest separating that into a separate sentence as shown. Sentences which go on too long are harder to read.

6/ You could get away with "graphic" as the adjective but "graphical" sounds better here.

7/ When talking about Morse code in English the long tones are called "dashes" rather than "lines".

This sound allowed of save life to many sailormen in the past,

I'm afraid I'll need to completely rebuild that one. Also this should be a separate sentence.

This sound allowed the lives of many sailors to be saved in the past.

1/ Taking the easiest bit first, the correct word in English is "sailor", not "sailorman". I think your confusion came from the similar word "seaman". There is (or perhaps was) technically a difference between the two (a sailor can handle a boat that is powered by sails) but it's an old difference and rarely used any more.

2/ You don't save the life TO someone, but OF someone. A life is something that they have. Something (in this case the SOS)  can allow you "TO save a life OF someone", but not "save a life TO someone".

Continued again...

Part 1 of the corrections

S.O.S

What does SOS mean?

This does not translate well when coming directly from Italian, unfortunately. In Italian this would of course be "Che cosa significa SOS?", which it looks like you translated literally. In Italian the verb significare (the equivalent of "means") does all of the work by itself. In English, however, you need an auxiliary verb as well. Specifically, the equivalent of "fare" in the sense of "to do". ("Does", in this case.) The general expression is "What DOES qualcosa mean".

Another way of expressing this using only a single verb (in this case the equivalent of essere) is "What is the meaning of SOS?" In this case "meaning" is a noun (sostantivo) instead of a verb.

It is Is the international way for ask help in Morse code since 1906.

1/ In Italian you usually don't explicitly state the subject of a sentence; "è il metodo internazionale... ecc" means "it is" etc; there is no need to explicitly state "it" as in "Quello è il metodo... ecc". However in English you do have to do that. However in this case I would not have used "it is" because that refers to something current; something which may not have a long history. It would be better to say It has been the international method... etc.

2/ The system was named after a person, Samuel Morse. In English it therefore needs to be capitalised.

Somebody Some people thinks that the three letters SOS are the acronym initialism of "Save Our Souls".

1/ "Somebody" would be a reference to one (as yet unidentified) person; roughly "qualcuno". "Some people" would be a group of non-specific people; very roughly equivalent to "qualche persone". Since "people" is a collective noun (roughly similar to "la gente"), you have to use the singular for "think".

2/ Don't worry, a lot of native speakers misuse the word acronym as well. An acronym is a set of letters (usually but not always initials) which are pronounced as a word; for example nobody says "N.A.S.A.", they say "Nasa". The same is true of "Qantas". However an initialism is where every letter is pronounced separately, like "T.G.V." (the train), "B.B.C" (the broadcaster) or "S.O.S."

3/ Since many people (represented by the word "our") would each have a "soul", it would have to be plural. That is, "our souls", not "our soul".

To be continued, as always with Italki's appalling character limits...