Are they ONLY used with nouns? I'm familiar with the rules you mentioned above, but when I write any sentence I'm not quite sure whether I should include an article or not. Please help me.
As far as I know there are lots of rules about articles. So In a short time, I will write everything about it. But don't worry. It is not hard. If you make some practice, than u will be used to using them in your sentences
I'm not a native English speaker. I know the rules like: an apple, a university, an honor, an hour etc. However, when I try making a sentence, I'm not always sure whether or not it needs an article. That's why I always avoid writing long emails.