usually speak (informal forms): 1) E aí, beleza? 2) E aí, tudo bem ? 3) Beleza? 4) Como vc tá? in English would be like "Hey, what's up?" the answer may be the tractional you've likely learned.. like: "Estou bem", "Mais ou menos", "Estou mal" etc.

Estou bem, obrigado(a). E você?

So... "como vai?" and "como está?" have the same meaning: "How are you?" In Portuguese it's usual to answer these questions with "beleza", or "tudo bem, e você?"... it's kinda like in English. "E aí" is the Brazilian version of "What's up?" haha, then you can answer like Denis said "Estou bem", "Mais ou menos", (...), "Não tão bem"...

vc = você *sorry for abbreviating