Dry fit the shelf.
Insert the shelf with the best side up into the slot in one of the leg assemblies.
Sand the tenons of the front upper and lower rail so they will slip into the mortise slot.
Apply glue to the mortise and tenon joints and assemble the table base. Make sure the table is square, that is, the joints are at 90 degrees.
Clamp and let dry over night. Use clamps on any joint you are gluing to pull the joint tight.
