English 'slang'

These are the most common examples.
GONNA = going to

I'm gonna watch TV tonight.
You're gonna like that.
I'm not gonna tell you anything.
It's gonna rain.
(it's necessary to use 'BE' - I'm gonna, you're gonna, he's gonna...)

WANNA = want to

I wanna hold your hand.
I don't wanna be late.
What do you wanna do?
He wanna eat.
Be careful. It's only 'slang'. Grammatically is correct 'WANTS TO'. However, if you are using 'slang' you can use WANNA

GOTTA = have got to

I gotta go.
Do what you gotta do.
I gotta tell you something.

You can use is also with HAVE:
I've gotta go.
He's gotta learn.

These are not so usual, but you can hear them.

OUGHTA = ought to
You oughta know.

KINDA = kind of
I kinda like it.
He's kinda funny.

LOTSA = lots of
It needs lotsa work.

OUTTA = out of
I'm outta here.
We're outta time.

GIMME = give me
Gimme that.

LEMME = let me
Lemme see that.

WHATCHA = what are you
Whatcha gonna do?

DUNNO = I don't know
I dunno.

SHOULDA = should have, COULDA = could have, WOULDA = would have
I shoulda never gotten married.
It coulda been worse.

AIN'T
This you can use for negative meaning of BE, HAVE

I ain't gonna do it. = I'm not going to do it.
He ain't listening. = He isn't listening.
You ain't my mom! = You aren't my mother.
I ain't done it. = I haven't done it.
She ain't got the money to buy it. = She hasn't got the money to buy it.
Only with this word you can use in 'slang' 2 negatives in one sentence. Of course, it's not grammatically correct.
He ain't got no money. = He hasn't got any money.
You ain't nobody. = You aren't anybody.
I ain't never been there. = I've never been there.

CUZ, 'COS, 'CAUSE = because