Points K and M are given on the lateral edges of a pyramid and point L on a side of the base. Let's draw the section without going out of the pyramid.

1. Draw the auxiliary plane SLB and the line segment LM in it, which also lies in the section plane.
2. Draw another auxiliary plane BCK and construct the intersection point of SL and CK, point E. This point belongs to both auxiliary planes.
3. Mark the intersection point of the segments LM and EB, point F. This point lies both in the section plane and in the plane BCK.
4. Draw the line KF and mark point N, the intersection point of KF and BC. This is the missing fourth vertex of the section.
5. All the four vertices of the section have been constructed; it remains to join them.