Go through it in approximately the sequence indicated, repeatedly coming back to this page. When you finish this force and motion stuff, go to fluids, heat, electricity and magnetism. Velocity and acceleration and all that, and the equations to use when acceleration is constant. In other words, it discusses the equations to use when the velocity Vs time graph is a straight line. Also the trig you need to know is included in that link above.
Forces are vectors.
The sketch above shows the horizontal 5 lb. For example if 3 lb. is perpendicular to the sum, then Pythagoras will tell you that the sum is 4 lb. The usual way to add the vectors above is by components. The square root of the sum of the squares of these is the magnitude of the resultant, 4. Try more vector problems .