If you have the question:
What is 2/3 minus 1/5?
You should start this question by looking at the demoniators (the bottom of the fraction). You want to get a number that is divisible by both 3 and 5. An example is 15 as it can be divide by both 3 and 5:
15/3=5
and
15/5=3
Now that we have picked our denominator, you need to change the number on top, the numerator. To do this, take the original denominator (3) and divide it by our new one
15/3=5
We now know that the numerator is out by a factor of 5. To make the fraction equivelant, you need to times the top number (2) by the factor (5).
2*5=10
Do the same with the second number and you should get the answer 3.
Now we have 10/15 minus 3/15=(10-3)/15=7/15 and we have our answer!