Mix a tub of mortar according to manufacturer instructions.
Spread a 3- to 4-inch bed of mortar evenly with your trowel over the concrete footer on which you plan to build a pier.
Set a block on the bed and press it firmly into the mortar. Place a second block, facing the same direction, against the first block. Press the second block into the mortar bed.
Lay your carpenter's level across the top of the blocks. If the level shows that the blocks are uneven, press down the higher block until it is even with the lower block. Tap the block with the handle of your trowel to make small adjustments. Fill both blocks with mortar for added stability.
Spread mortar atop the first two blocks. Turn a block the opposite direction of the first two and press it into the mortar. Place another block against the first and press it into the mortar.
Check for evenness with the level and adjust as necessary. Fill both blocks with mortar.
Continue adding mortar and blocks, with each successive course turned a different direction, until your pier reaches the desired height.