Turn the desk upside down so it's resting on its top. Assess the meeting points of the desktop and legs or bottom support posts. Corners will require L brackets, while straight joints will require straight brackets.
Position the bracket in place so it's touching both pieces of the desk. Mark the holes with a pencil.
Drill starter holes in both pieces of the desk where you marked the spots with a pencil.
Replace the brackets and drill the screws in place. There should be a bracket placed on the top and bottom of the legs or supportive posts and a bracket at both ends of the desktop.