1.I feel happy
> This sentence is correct.

2.I don't like study.
> I don't like studying.

3.She like's mirror.
>She likes mirror.

4.He help's my mom.
> He helps my mom.

5.I go to school
> This sentence is correct.

6.My friend like's banana.
> My friend likes banana. 

Alice, teacher has already explained to you how to use ('s) in a sentence. Please study more about this and always practice composing sentences. You are doing great! ^^

Take care and have a wonderful weekend.

~Teacher Cassie