Você means "you" in singular form. But it's conjugated the same way as the 3rd singular form (he, she, it - ele, ela, isto/isso)
- Você gosta de sorvete? (Do you like icecream?)
- Ele gosta de sorvete (he likes icecream)
Vocês means 'you' in plural (you all) and is conjugated as 3rd plural form, like eles/elas (they).
- Vocês/eles/elas gostam de sorvete (you [all]/they like icecream)
As Paulenrique says, it is rarely, if ever, used in everyday Brazilian speech, though you'll find it used in the Bible and prayers. This article says a little more: http://en.wikibooks.org/wiki/Portuguese/Contents/How_to_say_%22you%22_in_Portuguese
Why is "Vocês lembras" not correct?
Because it is Portuguese and not English?
Plurals are not the same from language to language (in fact, there are none in Mandarin).
"Vocês" is third person plural just like "Eles" and "Elas" and so this regular verb ends in "m" while the regular Portuguese verb ending for second person, "you" (which is "tu") has the "s" ending.
- Você lembra - 3rd Person Singular conjugation
- Tu lembras - 2nd Person Singular conjugation
- Vocês lembram - 3rd Person Plural conjugation
? I didn't assume there was a plural. Verb conjugation for Você ends in -as or -es normally. And now that I'm looking closer, I see this isn't Você, but Vocês, whose conjugations end in -am or -em normally.
So to answer my own question, the subject isn't Você like I thought it was.
Você conjugation does not normally end in "as" or "es" but rather the 3rd person, same as with Ele, and Ela (also being 3rd person) which is usually a vowel, so no "s" endings for Você either (at least not for regular verbs).
Tu however, which is the 2nd person for "you" does usually end in "s" conjugations.
Unless you are confusing "Vós" (2nd Person [informal] plural for "tu") which also conjugates with an "is" ending but, that is usually only used in the North of Portugal (along the border with Galicia from which Portuguese was born and that still uses "Vos" in everyday language (but now with a Spanish – Castilian – accent).
- Vós lembrais...
But "Vós" too is plural.