What is the actual cost of margin trading?

#1
Can someone explain to me what the actual cost of margin trading is?

I have a trading account with HDFC Securities and am given to understand that they charge 0.05% for intra-day trades. However, while trading today I noticed that they quoted a much higher brokerage amount in the "know your margin" section. Also, my available margin kept reducing with every trade though I was actually making some small profits!:confused:

Can someone please explain this to me? Thanks in advance.