1. You obviously have several options. Possibly the "best" move is 3.d4, and i think that the resulting positions can be played at low levels without much theory, simply relying on W easy development and piece activity. But if you want a less trendy option an idea is 3.c3 intending 4.d4, a sort of improved Alapin variation(2.c3) where B has not played the most energic counter. In this variation you usually get a nice centre to work with, and again an easy development.
The correct answer is probably: What do you play against other B second moves? Stick to something similar.
2. In the bloody strong nimzo indian defense both sides have several options. Common moves are, for example, 4.Qc2, 4.e3, 4.Nf3, 4.a3, just to name a few.
The popular 4.Qc2 has two ideas behind: allowing W to play a3 and win the bishop pair without spoiling his pawn structure, and enabling 5.e4. B has an impressive number of counters, including the sharp 4...d5,0-0,c5,Nc6. The nimzo indian is extremely complex and can't be explained in a few words. If you are really interested it's probably a wise decision to get a good book on it.
1.What should I do if my opponent play 1.e4 c5 2.Nf3 e6?
2.The opening moves 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 is called Nimzo-Indian Defence,what is the popular continuation?