Depends on the year and armrest type, there are at least 3. The early ratcheting rests use a triangular bracket screwed to the drivers seat frame. Useless without the bracket.
The most common are the middle years fabric ones (some rare ones have cupholders) that bolt to the tranny tunnel and often have a secondary screw hole that goes into a bracket inside the e-brake cover shich also has the hole. Sounds like you might have this type without the side holes in the armrest or in the e-brake cover?
The newest armrests are harder vinyl with cupholder trays and install on the e-brake cover top, but inside the cover you install a big heavy duty bracket bolted to the tranny tunnel. These rests are useless without that big bracket.