The simplest way to do this is with a calculator, as it can be very painful to solve by hand.
Most calculators have a square root key. Use that to find the root of a fraction. If using scientific/graphic calculators, put parenthesis "(" ")" around the fraction, e.g. "(1/4)".
And as for turning fractions into decimals, the easiest way is to divide using your calculator. If the fraction is 2/13, for example, remember that / denotes division. So enter 2 divided by 13 into your calculator and it should spit out .1538...