"falo" Only for the first person singular, "fala" Only third person plural, both for persons and objects, see below:
Eu - Falo Tu - falas Ele/Ela- Fala Nós - Falamos Vós - Falais Eles/Elas - Falam
"fala" is for third person singular "ele" and "ela" and it is also for "você" which means "you" (In Spain this form is formal for people older or above you in station or polite for strangers, but in South America "você" is used even instead of "tu" in some places.)
With slow pronounciation I hear "portugheis", with the fast one it seems it's "portughes". Which one is correct? Thank you
"portughes" is the correct version, but most people pronounce it like "portugheis".
Just curious because of the topic: Where is there a preposition in this sentence? Or am I missing an "elliptical", or implied preposition?
There is no preposition in this sentence, but some sentences in each topic simply introduce vocabulary. In English you could also say “ I talk in Portuguese.”, but it would be more common to say “I speak Portuguese.”