Locate the stud in your wall with a stud finder. Mark out where the bracket screws will go by measuring a line down the wall with your spirit level.
Then starting from the top down, screw in your vertical bracket. Use the spirit level to make sure the bracket is straight before you screw the last screws in. Repeat the same process for the horizontal bracket, marking the wall and using a spirit level to ensure the bracket is level.
Now loosely screw in two brackets to the top. Then flip the board and attach the board to the framework by fastening all four brackets. Now you can insert the drawers to finish off the basket unit.