Measure and mark the area where you are placing the vegetable garden. You will need both the width and the length.
Calculate the number of blocks you will need based upon your measurements. To find the number of blocks needed for a given side, divide that side's measurement by the size of a single cinder block. Add the results for all four sides together to get the number of blocks per course. Multiply that number by the number of courses you are building. A 4- by 8-foot bed requires 40 to 50 blocks.
Mark off the area with string and stakes. Set the stakes at each corner. Tie string around the stakes. Stretch the string between the stakes to mark the sides. Remove any debris, plants or material within the marked area.
Dig a trench around the perimeter of the garden. Make the depth equal to the height of a cinder block. Level the trench with a squared-end shovel or flat spade.
Mix the mortar in the wheelbarrow as directed on the bag.
Lay the first course of blocks in the trench. Lay the second course over the first course so each block spans two blocks underneath. Apply mortar between courses to secure the blocks together. Scrape excess mortar away using the narrow side of the mortar chisel.
Fill the base of the garden with gravel halfway up the first visible course of blocks. This will be the drainage for the garden.