I have HDFC trading account(though i am not big fan of this, I have only this account).
Margin order is used for day trading. Buy/sell in morning(uptill 2.30PM) and square off on same day(sell/Buy before 3.15PM).
Commission/Brokerage for this type transaction is .05 for each buy and sell(so net net, its .1+STT subject to minimum or 25
CnC is cash and Carry, Normal purchase of share and sell it on or after T+3(though it takes 4 days for share to reach ur account).
Comission/Borkerage for this type is .5 for buy and sell(so u buy and sell, all u pay comes close to 1.5%)
You can do day trading using CnC aswell for selected scripts. Here you can buy in morning and sell on same day where the commission is .1% for buy and sell(net net it comes to .4 including stt).