Can you not also say "Eu como quando quero"? In Spanish you can leave out "yo" "tu" "nosotros" because the verb conjugation tells you the actor. Is it the same in Portuguese or do you always have to put the actor with the verb?
Yes you can say it like that, but using both "eu's" adds more of a commanding tone. In English we would say it by emphasizing the 'I' - "-I- eat when -I- want."
How can you tell whether "como" means "I eat" or "like...". Is there a certain pronunciation? Or is it just context clues?
If it is the verb, 'como' means 'I eat'. If it is not the verb, it means 'like' or 'how'
"Como" also can mean "what" as in, "Como tu te chamas?" (how are you called?/what is your name), or just "Como?" which I liken to, "Come again?" but really just means, "What?" And yes, "like" as in similar.