Draw a line l and a point X on it. Through X, draw a line ssegment XY perpendicular to l.

Now draw a perpendicular to at Y. (use ruler and compasses)

Step 1: Draw a line l and mark a point X on it

Step 2: With X as center draw an arc to intersect the line at A and B

Step 3: With A as center and radius more than AX draw an arc. With B as a center and same radius draw an arc to intersect the previous arc at Y. Join XY

XY is perpendicular to AB

Step 4: With Y as center draw an arc intersecting XY at P and Q

Step 5: With P as center and radius more than PY draw an arc. With Q as a center and same radius draw an arc to meet the previous arc at M