You do not need a college degree to become a photographer. Fine art photographers often have MFAs these days, which means you need a bachelor's first, but this is not essential if you are simply trying to become the sort of photographer who, say, takes pictures of people. For that, working as an assistant to an established photographer may be all you need, though let's face it, a college degree could save your life if the photography doesn't work out.
Photojournalists often DO have college degrees and first honed their skills by working on their campus newspapers. They put together portfolios that way and then can present them to potential employers.
Taking some basic photography courses is a very good idea, but no, do NOT take these online. You won't get the instruction and hands-on training you need. You can ask an instructor how best to put a portfolio together.
If I were you, I'd go to college, major in something practical, but also take photography classes -- either in your college's studio art department or elsewhere. That will help you start to accumulate images for a portfolio.