What's the difference between "I'm gonna ..." and "I'll ..."

I think they might be a little bit different, but I am not so sure.
Could you generously give me some explanation or example?

Very slight difference. If someone uses "gonna"..there tends to be more weight behind what they say...it's just putting a little more emphasis on their intended action I guess. Eg..which sounds more threatening: "I'll Kill you" or "I'm gonna Kill you"..I think the latter

I am going = i gonna ,that is the immediate futurI gonna do it and i start rightnow.
I'll do it= i shall do it maybe tomorrow or next year.

Just like all the sheep said, when you use "gonna" it means the action shall occur right after the sentence be said or you're really determined to do what you say.

Will is about something that u are not sure in future
but gonna(going to) is about sth u are sure
For example you meet your friend then he says ' Do u know Peter is in hospital? he had an accident. So he says "I'll go and see him.
Because he did not plan it before
But if you have decided to go to a trip two days ago , you say I am going to a trip.
Because you have decided before.

"I'm gonna" is low class, like "youse" Don't use either if you wanna be taken seriously That's "wish to be taken seriously."

Youse walk on four legs
And I walk on two
The last ewe that I saw
Looked just like you.

One day I'm gunner be a gunner and I'm gunner gun yer down.

"Gonna" is used all the time colloquially in the US. I wouldn't call it low-class. I say it all the time, but I definitely wouldn't use it in a job interview. It's hardly in the same category as "youse," which also isn't necessarily low-class, but is basically a geographically restricted expression.

In the U.S., "gonna" is very common in colloquial speech and isn't considered low-class. Like Ryan, I use it all the time and I certainly don't consider myself a low-class person. "Youse", on the other hand, sounds terrible to my ears and is stigmatized as low-class.

I'm gonna is the American way of saying 'I'm going to'. This expresses an intention, a plan. It's expresses a decision made before the moment of speaking.
I'll is also used for a decision, but it is spontaneous, made at the moment of speaking.

''Gonna'' is a nonstandard spelling of ''going to'' just like ''hafta'' is a nonstandard spelling of ''have to''. They're slangly spelled this way because that's how they're often pronounced.

"Gonna" isn't really considered low class in the US by most, but to me it doen't sound very nice, however, it is generally acceptable for informal speech. The "lower-class", or even less formal version would be "I'm'a" as in, "I'm'a go for a ride, wanna come?". Sloppy as that may seem to those not accustomed to hearing it, it's not perticularly uncommon, (in informal speech).

"Im'a..." This sounds rather "hickish" to me.