Measure and mark the selected area for the fire pit with landscaping spray paint. Paint a circle that is the diameter that you would like for the fire pit. This is the outside edge of the pit.
Dig a 6-inch wide trench that is 8 inches deep along the inside of the painted circle with a shovel. This is the area for the fire pit foundation.
Fill the first 4 inches of the trench with sand. Dump gravel into the remaining space in the trench so that it is level with the surface of the ground.
Tamp the gravel down with a plate compactor to create a smooth and firm foundation for the first layer of bricks.
Lay a three-brick wide layer of bricks around the foundation of the fire pit. This is the base layer of bricks. Check the evenness at various points around the base layer by placing a level on it. Adjust for level by tapping the bricks with a rubber mallet. Stagger the bricks so that the joints fall in the center of the adjoining brick.
Mix the mortar in a mixing trough with a trowel as directed on the mortar mix package.
Apply a layer of mortar to the bottom of the bricks as you place them onto the base layer of bricks. Stagger the joints so that the center of the top brick falls over the joint of the bricks below. Build the brick fire-pit wall in this manner until you have reached a height of 18 to 24 inches. Allow the mortar to set.
Fill the inside of the fire pit with a 6-inch layer of gravel. Insert the metal fire pit liner into the center of the pit.