When making an outline. i have my main idea but i need coming up with a supporting idea.
my main idea is: benefits of taking online college classes.
then i need my supporting idea:

ps. i'm not any good at english this is my worst subject next to math.

Maybe compare and contrast online schooling to regular schooling, then lead into the idea that online schooling provides you with many more resources than just a teacher could, plus it allows for a different learning style. Then conclude with your main point and maybe one fact about it

I suppose as supporting ideas (reasons) you could put are that online college classes are convenient because you could virtually take them anywhere as long as you have a computer, they allow for those who don't do well in social environments to do well in school and if you have a busy schedule you could take online classes whenever you have time.