On Coinome’s exchange page, under ‘Buy BTC’ section, you will find 3 boxes called Volume, Price and Amount. This refers to the Volume of BTC you want to buy, the price you are willing to pay, and the total amount in INR, which is equivalent to Volume * Price. You need to enter any 2 of the 3 boxes, and then click on Buy.
If the buy price matches an existing sell order, the order is executed instantly. Otherwise the order remains in the open order book, till a seller comes and matches it.