[Dalek]

You raise in no limit hold'em for several reasons:
-better hand call
-worse hand fold
-charge a drawing hand
-obtain information
-block your opponent from betting a larger amount when you want a card/showdown cheaper
-make a worse hand fold but increase your overall chance of winning the pot

C-betting is betting the flop after you bet pre-flop and can be done with a strong hand, semi-bluff or pure bluff.

Generally people C-bet when they miss but this isn't always +EV, especially at micro-stakes where bluffing is much less likely to be successful.

Betting on the flop with different holdings does disguise your hand but this isn't too important in micro-limits.

As i said, the gap concept doesn't apply between betting rounds because of the difference in information available.