To 'learn' something is the process of knowing something for the first time, after not knowing it. For example: if someone tells me something I didn't know before, I learned that piece of information. To 'study' something is to actively sit down and learn or practice it for a period of time. "I study.." and "I learn..." mean you do something generally, but not necessarily right now. When you are talking about an academic subject, like English, it's easy to see why these can mean pretty much the same thing (as they do in your first two sentences). If you say something like "I learn something new everyday", you can see that 'learn' definitely does not mean 'study'. Adding -ing to a verb changes it into an adjective and/or noun (you can use it as either, depending on the situation, but in the context of present continuous they're exactly the same anyway). 'I am studying' means that as you speak, you are studying. It's the same concept for 'I am learning'. Since this form only refers to now, the difference between 'learn' and 'study' is much more distinct.

Your first and second sentences mean the same. They both mean that you "study English" on a regular basis. On the other hand, your third and fourth sentences mean that you are currently "studying/learning English".

There are not any difference between the first and the second sentence. Both of them mean that you study English regularly. With regards to the third and the fourth sentences, they mean that they are your temporal activities. You I studying English just now or you are learning English for a short period of time.