When we have the same denominator in our fractions we need only add the numerators then put the result over the common denominator. If necessary we can then simplify it to lowest terms or a mixed number.
When we have unlike denominators, our first step is to find equivalent fractions such that all of the denominators are the same. We find the Least Common Denominator (LCD) then rewrite all fractions in our equation to equivalent fractions using the LCD as the denominator. Now that all denominators are alike, we solve the equation of fractions with like denominators.
For these and some more basic methods of working with fractions see also Help With Fractions.