Can someone please teach me how vosotros is used?
For present indicative, regular -ar verbs use -áis. e.g., escucháis.
regular -er verbs use -éis. e.g., entendéis.
regular -ir verbs use -ís. e.g., escribís
reflexive verbs use "os" as in "os laváis"
Irregular ones are, well, irregular. Ser, for example, becomes sois.
Preterite uses a form that sort of looks the one for Tu, but has an -is on the end, as in fuisteis. For most of the other tenses, take the Tu form and sneak an "i" in just before the last "s". e.g., seréis. That's a bit of an oversimplification.
For the compound forms, haber becomes habéis, habíais, hubisteis, habréis, or habríais, depending upon which one you want to use.
You should visit reverso conjugator on-line and just look at them. For example, http://conjugator.reverso.net/conjugation-spanish-verb-escribir.html
Don't count on getting it "correct" in duolingo, though. A few times I used vosotros and the appropriate verb for translations from English to Spanish, just to mix it up a little, and I was counted wrong. I think if you report it then it may eventually get added, but many exercises don't accept the vosotros translations yet.