Det är min första tid gång att skriva på svenska

Hallå! Jag heter Fionn och jag kommer från Irland. Jag gillar att simma för och jag arbetar som livräddarena på stranden i Irland. Jag vill lära mig Svenska därför eftersom att jag kommer att hälsa på i Sverige i ny nästa året. Här i Irland, det är det så kallt nu. Det kommer att vara bli jul snart.

You can also change this sentence to:

Jag gillar att simma för och jag därför arbetar jag som livräddarena på stranden i Irland.

"I like to swim and that's why I work as a lifesaver on the beaches in Irland."

 You can change it to:

Julen är påväg.

"Christmas is comming."

Blue: Added words

Orange: Changed words (look where i used the underline, that's what i changed)

Green/Purple background: Other ways to write the sentence

Crossed words: Words that shouldn't be there

I think you did a very good job on writing in swedish and I hope you understan how I've corretcted your entry! A tips for next time, also write what you want to say in english! That way, swedish people can easily see what you want to say and correct any mistake. :D

I am helping my professor, and I am  is almost done. 

3 months ago, I've started began to help my professor write his paper as a part-time job.

What do you mean by "write his paper"?

Do you mean that you are helping him correct homeworks or something like that?
And after 3months later, It will be done helping him!!

Now I'm doing a final (or) finish work (I don't know how to say it) (for him) and then, We're going to fix it.  correct the paper.

I can't help you with this sentence, because I don't know what you are trying to say. But to make the sentence better, use final work, and if you are doing it for your teacher, add "for him". And by "fix it" i assume your talking about correcting your paper?

Because of this work, I couldn't be using can't use Skype and this web-site.
I can't stand not talking with to my friends!! haha 

If you don't have "not" in the sentence, you'd be saying that you don't like talking to your friends, which I assume you do.
Thanks for reading my diary haha

I hope you understand my notes ^^ 

Blue = Added words

Grey = Deleted words

Orange = Can't understand what you're meaning

Pink = Notes

I am helping my professor, and I am almost done. 

3 months ago, I began to help my professor write his paper as a part-time job.

And after 3months, I will be done helping him!!

Now I'm doing a final work (for him) and then, We're going to correct the paper.

Because of this work, I can't use Skype and this web-site. 
I can't stand not talking to my friends!! haha 

Thanks for reading my diary haha

I took a middle-term

From last week, I took a middle-term at school.
At that time, I really had a hard time to studying and do my part-time job at the same time.  
As far as I know, western students are doing have a part-time job aswell.
Does Is it too hard to do both of them at the same time?
I wonder what their their school-life is like haha.
And I'm going to have dinner with my girlfriend tonight.
And we are going to eat steamed clam(?)
Hmm Have you eaten that kind of food? It is really suited these days. haha
Thanks. Have a nice day!!

Corrections

Added words

Great job! Is sounds delicious with clams! I hope you have a nice evening! ^^