"We feel very happy."
Translation:Nos sentimos muy felices.
Good question. "Nosotros" simply means "us" in English; other related forms would be yo, tú, ellos, etc. You could actually put that at the very beginning, but it's normally omitted because it's a bit redundant.
The verb here is "sentirse," and the conjugated form requires a specific reflexive as well; in this case, it's the "nos" placed before the "sentimos." Search on the reflexive forms for more info.