There are very nice online courses, for free you can find some basic concepts, sometimes intermediate, but for any advanced, you'll need to pay, unless you prefere reading, and there you can find good articles in forums, just like here.
But not all online courses are great, some of them, are overated and too pricy, for what you get. The best is to find ppl to study with, or a coach, the first is difficult, I find myself working with one person like 1 week, and then he stops playing poker, or studying, same the next week, so not easy to find motivated ppl, the second choice costs a lot. Good poker coaches can take up to 1k/h , but you still can find some nice coaches with 50$/h , they won't take less, unless you know them personnally, as they would prefer make it at poker tables. So the online courses are very nice medium.