Hello, daurelie, welcome to the source of great wisdom that is this board - although not emanating from me, I hasten to add; I am one of the clowns.

I don't think there is an easy answer to your first questions. I used to teach basic literacy and always found it difficult to deal with similar queries from those I was working with.
The second part of your question is a little easier, perhaps. All good dictionaries include information as to the part of speech of each word, with examples where there are several possibilities. Reading, marking, learning and inwardly digesting will give you a good idea over time - but it isn't going to be a fast-track.

To find out about correct usage, I don't think you can beat an evening class on English Grammar, if you can find one, and afford both the time and the money for it. There are "Teach Yourself" books out there, but I cannot offer an opinion on them as I have never looked at one.

Reading books by reputable authors is also a way of increasing your word-knowledge. Try Winston Churchill's History of the English speaking People. The historical content is contentious, but the story-telling is great, and Churchill's use of language is exemplary.
But there are plenty of other author's who are lighter in style whilst still using very good English - Stephen King is a good example, so is Dick Francis.

Of course, you could just keep reading and contributing to AWAD Talk !