For some mental illnesses, such as severe agoraphobia, you may be able to find some online sessions for treatment. Eventually you will have to see a therapist in person though. It's difficult to do therapy over the internet. For a therapist to be truly effective they need to watch you in person and see how you react to things. You're better off going to see one in person.
If you just want general psychology information, you're better off using google scholar and searching key words for what topic you are looking for.