Multiplying two decimals together is not more difficult than multiplying two integers together.
The first step is to multiply both numbers together as if they were not decimals. Imagine that both numbers do not have decimal points and simply multiply them.
Once you have a result we must find how the decimal fits into the answer. To do that we start by counting up the total number of decimal points in the operands. In this case 2.57 has two decimal places and 6.2 has 1 decimal place for a total of 3 decimal places. In our answer we start at the right and move over the total number of decimal places in our operands, in this case 3.
We get a final answer of 15.934.