The denominator is the bottom portion of the fraction. Example 4/6, the 6 is the denominator. The easiest way to start out in finding the common denominator is to see what number, 8 and 14, go into equally. Example: 1/4 and 1/3, 3 and 4 both go into 12. If you multiply 4 by 3 as well as 3 by 4 you get 12 both times. Now try it with 8 and 14.
In addition and multiplication, it does not matter which two numbers you put together first. On the left aide 6 is associated with 3. On the right side 3 is grouped with 7. It doesn't matter where 3 goes. You still get the same answer.