Ich studiere Deutsch als meine zweite Fremdsprache an der Uni. Ich hab' auch an der vorhergehend Uni Deutsch als die Hauptfremdsprache studiert. Das gab mir Hoerverstaendnis von der Sprache, aber ich mit sprechen(?) noch ringe, weil mein Vokabular sehr klein ist. P.S. (Englisch) An advice I've seen from Germans online is to use "du" unless you know you're talking to a person of higher social standing (an older person, your teacher, an official of some sort, other formal occasion). Addressing a regular person online with "Sie" is seen by a native as too formal, which is undesirable in a relaxed conversation. So, everyone on Hubski will address each other as "du", and so should, according to the advice, people of Reddit (where, despite the astonishing range of social standings people bear, it doesn't matter). Addressing an unfamiliar person of about the same age with "du" in a social network message went fine for me, and so did addressing an obviously-older unfamiliar person with "Sie". P.P.S. Der Titel muss "Wer hier Deutsch lernt?" sein, oder?
Slightly related, the Wikipedia article about the Swedish du-reformen is surprisingly well written.