Where can I earn college credits online?

If you have a local state college or junior college they typically offer online classes.
Go to their website or make a meeting with a councelor. This is how I did my last 8 credit hours and that was quite a few years ago.

What @risingonashes said. Take the classes from an accredited institution that has a brick-and-mortar campus with a significant student population. Online-only colleges tend to be expensive diploma mills, and a degree earned from one of them will not be accepted a lot of places.