What is the different between … ?

1. Get out, come out, go out;

One easy way is to remember "get out" implies you are forced.  "come out" may be on your own or by invitation because something out there is nice. "Go out" is getting out to have something nice.

Get out before it is too late. Get out of my place for you are no longer welcomed in my home.

Come out and play (an invitation)

Come out when the sun is out (because the sun is nice)

Come out wherever you are hiding. (Depending on tone and context, this "invitation" may be a command)

Go out and have fun. Go out of the house once a while will be good for you. Go out and have a drink (Go to a bar/restaurant and have something alcholic)

Go out into the world and find your fortune.

Get out into the word and find your fortune. (this is more like a command and be forced to go out).

2. Get back, go back, come back, be back;

Get back: means revenge.

You are at "X"

-----------A------------------X--------------------B

Go back: From X to A

Come back: From B to X

I will get back at you for that dirty trick you played on me.

Go back where you came from. (You are at X.  Return to A)

Come back to me.                    (You are at B, return to X).

3. Go down, come down;

You are at "X"

-----------A------------------X--------------------B

Go down is from X to A.  Come down is from B to X.

Please go down to the cellar to bring some wine up.

Please come down from the loft and bring some me the book that I had left there.

4. Turn around, look back;

Turn around, your body turns around or you return in the opposite direction.  "Look back" literally means turn your head or body just to look or thinking of something in the past.

You better turn around before it's too late!

I look back at the fond memories of my childhood.

5. Possible, perhaps.

Possible: Able to be done; within the power or capacity of someone or something.

Perhaps: A more formal term than "may be"

It is possible to fly on your own if you are born a bird.

Perhaps, if you would be so kind to move the picture a bit further to the left.

I will be grateful to you, if you give me examples.

Good questions.