Scalars and vectors:

A scalar has magnitude. Temperature (30 degrees C), length (4 inches), volume measure (a cubic yard), etc. Only a number is needed to describe the measure of the quantity.

A vector has magnitude and direction. Velocity (20 mph, due East - note that the magnitude of velocity is used often enough to warrant its own name - speed. Most vectors aren't this special), force (you can't apply a force without am associated direction), etc.

To deal with vectors (and many other things), we need to establish a reference system from which to make our measurements. We choose an orthogonal coordinate system with axes defined by the right-hand rule. More about coordinate systems later - for now, we need some ways (mathematically) to deal with vectors - click here for starters.