There is an important acronym to use when multiplying binomials.

FOIL stands for:

First - Multiply the first term in each parenthesis.
Outer - Multiply the outer term in each parenthesis.
Inner - Multiply the inner term in each parenthesis.
Last  - Multiply the last term in each parenthesis.

FIRST: Now lets give it a try in our problem. We'll start by multiplying the first term in each parenthesis and then marking down the answer below the problem.

OUTER: Now we will multiply the outer terms and again mark down the answer below the problem.

INNER: And the Inners.

LAST: And finally the last terms.

Now as you can see the results from the multiplying of the two inners and the two outers are like terms. Our last step is to combine these like terms.