I haven't even done any "past tense" lessons yet... isn't the -amos ending for both present and past tenses?
Yes, it could be "we speak" too.
The same rule applies in Spanish as well.
-amos is to indicate plural. The past tense would be falávamos (so "-ávamos").
"-ávamos" is a past continuous, while "-amos" is eighter present or simple past.
"Falamos" can be either present or past tense.
When written in the simple past, shouldn't it include an accent mark as in "falámos"?
This is the case for PT-PT. For PT-BR, the it is the same.