Multiply the figure by a decimal, equivalent to the percentage you are trying to find.
For example, to find 75% of 200, you would type into your calculator 0.75 X 200, which gives 150.
If you find it hard to work out the decimal, an easier (but slightly longer) way of doing it is to divide the original number by 100 to find one percent, then multiply by the number of percent you're trying to find.
For example, to find 63% of 124; do 124/100, which is 1.24 (one percent). Then multiply 1.24 by 63, which gives 78.12.
Hope that helps?