How to draw a line parallel to a given line ??

dear student,

take a point outside the given line.(P)

join that point to any point on the line.(Q)

whatever the angle made by this line  segment PQ with the given line, we have to construct its alternate  equal angle .

Join P with the intersection 

(R)

of the arcs drawn during constructing this angle.

join PR.

This is the line parallel to the given line.