
Start with a line segment PQ that we will copy. 

Step 1 
Mark a point R that will be one endpoint of the new line segment. 

Step 2 
Set the compasses' point on the point P of the line segment to be copied. 

Step 3 
Adjust the compasses' width to the point Q. The compasses' width is now equal to the length of the line segment PQ. 

Step 4 
Without changing the compasses' width, place the compasses' point on the the point R on the line you drew in step 1 

Step 5 
Without changing the compasses' width, Draw an arc roughly where the other endpoint will be. 

Step 6 
Pick a point S on the arc that will be the other endpoint of the new line segment. 

Step 7 
Draw a line from R to S. 

Step 8 
Done. The line segment RS
is equal in length (congruent to) the line segment PQ. 
