Measure from end to end on the towel rack (ours is 19-1/2”). Then measure the desired height on the wall where the towel rack will hang.
Make two small vertical marks on the wall spaced apart the length of your towel bar (again, our marks are 19-1/2” apart).
Use a level to make two horizontal marks that intersect with the vertical marks, creating a "+" sign.
Hold up the mounting plate and align the top hole with the "+" sign. Use a pencil to mark both bracket holes. Repeat this step for the other side.
Use a 1/4” drill bit to pre-drill holes in the drywall where your pencil marks are drawn.
Hammer in the drywall anchors. (They're normally provided with the towel bar.) Secure the mounting plates to the wall using the provided screws.
Line the left side of the towel bar up with the mounting plate and push in towards the wall. Repeat this step for the right side of the towel bar and pull down firmly on both sides to lock the towel bar into place.
For clarification, on the back of the towel bar there should be a label that identifies which side should go up and which should go down.