The magnitude of a vector is its length. The magnitude informs you how fast something is traveling, while the direction tells you where it's heading.
The magnitude of a vector is simply the square root of its components' sum. Because 32 + 42 = 25, the vector:3,4> has a magnitude of 5. The magnitude is 5 since 25 squared is 5. (units).
It has a radius of one and all unit vectors have the same magnitude.