Courtney, you must have misunderstood your teacher, at least a little.
1/3 is never equal to 3 or any other whole number. However, it is equal to 0.33333... with the 3 repeated forever.
In the same way, 1/2 is never equal to a whole number. It is equal to 0.5, which has a decimal but not a fraction. You could multiply by 0.5 the same way you multiply by 5, except that you might have at least one extra decimal place in the answer.
Example: Suppose you want to multiply 16 by 1/2. Change the 1/2 to 0.5 and set it up this way:
8.0 (or just 8)
Any fraction can be changed into a decimal by dividing the denominator into the numerator and carrying it out as many places as you wish. Just remember to keep track of where the decimal point should be.