How do you add or subtract fractions in real life?

I do it by finding a common denominator.

For example, 2/3 - 1/5.

The least common denominator is 15. 2/3 = 10/15, and 1/5 = 3/15, the difference of which is 7/15.

Here is another example:

5/6 - 2/3. In this case, the least common denominator is 6.

2/3 = 4/6, and 5/6 - 4/6 = 1/6.