This is where the translation of "ka/ke/nå" as "the" breaks down. Polynesian languages don't have definite and indefinite articles the way most Indo-European languages do. What they DO have are "noun markers" which are used far more consistently than articles in Romance or Germanic languages. Nouns always need to be preceded by some kind of noun marker, as the distinction between "parts of speech" is far more fluid, so they're needed to contextualize that we're dealing with a noun, rather than a verb, and adjective, etc.
I normally peruse Wikipedia as a great starting point for introductory grammar. Then, I look for the references and links cited and follow through on using those if I can. It's been a very helpful tactic for me :)
yes, e plays two different roles! the first is like you said, to make a command or suggestion, and the other is to address someone. here's how the tips and notes define it:
E is used before an action to signify a command or a suggestion. When you say, "E hele!", you're telling someone to "Go!"
E is used before a noun (usually a person) to indicate that the person is being addressed.
Ex. Mahalo, e Kawika. (Thanks, Kawika.) ➜ You are saying thanks to Kawika.