A reference angle is the acute angle (<90) formed with the x-axis and the larger angle.

For example, a 220 degree angle can be represented by drawing a ray on the positive x-axis and a ray in the third quadrant. The ray in the third quadrant makes an acute angle of 40 with the x-axis. If you draw this out you should understand it pretty easily. The reference angle is always less than 90 degrees and it is between the x-axis and the second ray(the one not on the x-axis) in the larger angle.

Here are some of the formulas you need - your book should list the subtraction ones (or just let v be negative) - or search on wikipedia

sin(u+v) = cos(u)sin(v) + sin(u)cos(v)

cos(u+v) = cos(u)cos(v) - sin(u)sin(v)

Here is an example:

cos(u)cos(v)-sin(u)sin(v)=cos(u+v)

let u=80, let v=10

cos(u)cos(v)-sin(u)sin(v)=cos(80)cos(10)-sin(80)sin(10)=cos(80+10)=cos(90)=0