On the subtraction, you have to find the common denominator and then only subtract the numerator (top numbers). On addition, you do the same thing. On multiplication, you can just multiply top numbers by the other top number and denominator by denominator and reduce it down to it's lowest common multiple.
Example: 9/6 x 3/6= 9x3 and 6x6= 27/36, and you can reduce it to 3/4 because they both divide equally by 9.