Determine how many caps you'll need based on the length measurement of the wall. If you want to cap brick columns, you'll need to purchase pre-made caps in the appropriate size. Caps, or brick coping, often feature a rounded edge to enhance the look of the wall.
Mix a batch of the same mortar you used to complete the wall according to the manufacturer instructions. Apply an inch-thick layer of mortar to the underside of the cap or brick, then press firmly down onto the wall. If using a coping brick, make sure the rounded edge is facing in the direction you want it. Check the cap with a level to ensure it is evenly applied to the wall or column.
Smooth out mortar lines between the caps using a concave jointer if you're using bricks or other individual stone materials.