Make sure the denominators of the two fractions are the same. The denominator is the bottom number of the fraction. For example in 1/4 the denominator is 4, and in 1/2 it is 2. If the bottom numbers of the fractions are not the same, the easiest way to get a common denominator is to multiply the denominator numbers together. So in the example above, multiply 2 by 4 and you get 8.
You must then multiply the top number by the same number you multiplied the bottom by. So the 1 in 1/4 is multiplied by 2, and the 1 in 1/2 is multiplied by 4. You now have 2/8 and 4/8.
Believe it or not, that was the hardest part! All that's left is to add the fractions together. When you add the fractions together, the bottom number should stay the same. In our example, the 8 stays the same.
Add together the two top numbers. In the example, 2/8 + 4/8 is 6/8 (or ¾ if you simplify).
If you end up with a number on top that is larger than the bottom, you can convert to an improper fraction, but it's easier to just leave it in the form of a fraction. Find some workbooks or make up some examples to try.