what's the difference between 'pran fil' and 'pran kouran'

Pran fil →succeed, flourish, take off, to get the hang of, to become proficient 

Li fèk koumanse bizinis la, e li gentan pran fil.
He just started the business, and it's already taken off.

Li fèk jwenn travay la, e yo gentan pwomote l kòm manadjè.  Li pran fil nèt.
He just got the job, and he's already been promoted manager.  He's flourishing.


Pran kouran → to receive a jolt, to receive an electric shock, to get a sudden bolt of energy

Lè mwen te manyen manch pòt frijidè a, mwen te pran kouran.
When i touched the handle of the fridge door , I got shocked.

How would you say sentences like: You're not that bad, She's not that pretty, He's not that handsome, etc...

Use:  Pa pi identifier pase sa.
or
Use: konsa

You're not that bad.
Ou pa pi mal pase sa.
Ou pa mal konsa.


She's not that pretty.
Li pa pi bèl pase sa.
Li pa bèl konsa.


He's not that handsome.
Li pa pi bo gason pase sa
Li pa bo gason konsa

Mwen kwè → I believe

How do you translate preposition 'in" in sentences like: His life is in danger. You're in good health.

Adverbs?
In that case, you can say 'an'

His life is in danger.
He's living unsafely
Lavi li an danje.


I'm in good health.
I'm healthy
M'an bòn sante.


You're in good health.
You're healthy
Ou an bòn sante.


They got married secretly
Yo marye an sekrè.

Mandaly, ki kote w soti?

M fèt Kafou, m leve Akayè.

I know how to say 'thanks' in Creole. How would you say 'Give thanks to the one who gave us this beautiful day.'

Give thanks...
Di mèsi...
Bay remèsiman


We're giving thanks.
N'ap di mèsi
N'ap bay remèsiman
Nou pote remèsiman


Give thanks to the one who gave us this beautiful day.
Bay remèsiman pou sila a ki ban nou bèl jounen sa.

Can u confirm that creole JENES means young person and prostitute? if yes how do you differentiate them?

Yes, you are right the Creole term 'jennès or jenès' both would translate the English words youth and prostitute.
The meaning is in the context.

'Ou pa mare pye lanmò' would mean exactly ... Thanks!

Ou  pa mare pye lanmò.
You can't cheat death
or
You can't stop death.

ANY MANNERS I SHOULD KNOW BEFORE GOING TO HAITI FOR A MONTH STAY??

See these two links.
Terms of respect
What's considered rude

mwen ap ale m' menaj lakay...(girlfriend)is that correct? mesi :)

That sentence is not grammatically correct.
Did you mean to say  'I am going to visit my girlfriend.'?

There is joy...

There's joy...
Gen jwa...
Gen lajwa...

I want...

I want ..
Mwen vle...


I would like...
Mwen ta renmen....

How do you say seven?

seven - sèt
seventy seven - swasanndisèt

do voodoo really works? i heard that haitian are very powerful in voodoo.

I heard that too :)

Haitian vaudou is not magic, and it is not a spell.

It is a religion.

Nou pa la. (We're not home.)?

Nou pa la.
We're not present.
We're not home.


Nou p'ap la.
We won't be home.
We won't be there.
We won't be present.
We won't show up.


N'ap la.
We'll be there.


M p'ap la lè sa a.
I won't be there at that time.
I won't be available at that time.