Dry fit (called dry bonding) the first two courses of bricks, alternating the stacks so you know how to lay them down. The next thing to do, is to mix your mortar. Open 2 of the 6 bags of Quickrete Mortar mix (containing sand) and pour them into your wheelbarrel. (only two at this point because you don't want your mortar to set up (harden) before you can use it) Pour in water per package instructions and begin to mix with a shovel until the consistency of heavy oatmeal and there are no more dry particles. Spread mud around the edge of your base (two blocks) using your trowel be sure to spread the mud out to the edge of the block about the width of a brick. Begin laying bricks atop the mud (don't push them down too far at first, it's better to have too much mud under them before leveling, than not enough, too much and you can tap them down removing the excess squeezed out mortar with your trowel, too little mud and you have to remove the brick, relay your mortar and basically start over) Lay each brick on the course before using the level at the end, start from your first corner layed and level each side all the way around in a circle, gently tapping the top of the level with the handle of your trowel to get each brick to "settle" downward. Keep going all the way around your course leveling and tapping until you have done your first corner over again. Next level from corner to corner, then use your square to check the corners, gently tapping the brick with the handle of the trowel to move them slowly. To double check the square, measure the distance diagonally with a tape measure, both measurements should be equal corner to corner. You want approximately 3/8" joint between courses and between bricks (bed joints horizontal and head joints vertical) Congratulations, you've just layed the first course of your new mailbox! Now continue up to the next course by spreading mud and laying down a new course of brick, level, square, continue.