You need to multiply each term of one factor to every term of the others.
For example, (a+b) (c+d)
Multiply a to c = ac
multiply a to d = ad
multiply b to c = bc
multiply b to d = bd
So, (a+b) (c+d) = ac + ad + bc + bd
Note that you may combine constants and similar terms.
Similar terms are those with the same variables raised to the same power.
Example: x² + x² = 2x²
