Unit vector generally refers to a vector of unit length (i.e. its length is "1"). A direction vector usually points from a source point to a destination point.
A unit vector has a magnitude of one. To derive the unit vector from a direction vector (or any other type of vector) you divide the vector by its modulus.
if V = ai + bj + ck, then the modulus is V' = SQRT(a*a + b*b + c*c)
A vector is a line that has magnitude and direction.
A scalar is a line that has magnitude only.
Normal to a plane means a line that passes through a plane at a right angle (90 degrees) to the plane. The leg of a table is normal to the plane of the table.