There's the StackExchange English Language Learner's board - ell.stackexchange.com; while not an English or liguistics expert, I participate there, and questions on articles are common.
- English generally wants singular nouns tagged with a determiner unless the noun is being used to refer to the type of something rather than an instance of something, or in more than a few fixed prepositional phrases.
- Determiners, including articles, signify the importance and expectation around the question "which X".
- Definite articles are a signal to the listener/reader that the they should know which X the speaker/writer means. That's all. It has nothing to do with "specificity" as often explained by others. If the listener/reader doesn't know typically they will be triggered to ask.
- The indefinite article is a signal to the listener/reader that they don't have to know or care about "which X". It will trigger a listener/reader not to ask or wonder.
- Proper nouns don't take articles because usually the question "which John?", for example, isn't a concern.
- English generally wants singular nouns tagged with a determiner unless the noun is being used to refer to the type of something rather than an instance of something, or in more than a few fixed prepositional phrases.
- Determiners, including articles, signify the importance and expectation around the question "which X".
- Definite articles are a signal to the listener/reader that the they should know which X the speaker/writer means. That's all. It has nothing to do with "specificity" as often explained by others. If the listener/reader doesn't know typically they will be triggered to ask.
- The indefinite article is a signal to the listener/reader that they don't have to know or care about "which X". It will trigger a listener/reader not to ask or wonder.
- Proper nouns don't take articles because usually the question "which John?", for example, isn't a concern.