"I'se" is acontraction in African-American English of "I is" which, in standard American English, would be "I am". A common use of "I'se" is to form the phrase "I'se going to ...." which means "I'm going to....". Hope that helps.

It's a thick dialect form of "I am" (the speaker is actually making a contraction of "I is"). Depending on context, it can also mean "I was" or "I has". Good to know it exists, but the fact is you'll never use it.