When you multiply fractions, say, 2/3 and 4/5, the numerators and denominators are multiplied, such that 2/3 * 4/5 = 2*4 / 5*3 (which is 8/15).
When you multiply whole numbers, say 3 * 4, you are essentially adding three together four times, such that 3 * 4 = 3 + 3 + 3 + 3 (or 4 + 4 + 4)
When multiplying fractions you can multiply both numerators and both denominators:
1/3 * 5/4 = 5/12 (5*1 = 5 and 3*4=12)
When multiplying whole numbers you take the number and add it to itself the amount of times the other number says:
2*3 ... 2+2+2 (cause of the "3" do it three times) or 3+3 =6
