How do I use self-drilling and tapping SS screws?
Do yours look like this?



The straight portion of the shaft doesn't have to be as small as the pre-drilled pilot holes in the poles.  Notice the angled point and the lip ("flute") along the edge: that's a built-in drill bit on the tip of the screw. It will open up the hole to the diameter it needs.  The pre-drilled holes in the poles are there to start it out straight, in the right place; the screw will do the rest.

The hex head doesn't have a screwdriver slot because it is designed for a socket wrench.



It's very common for the heads on these screws to fit a US 1/4-inch socket.

Get a socket wrench, or a socket driver adapter for your drill, and go for it.  It'll work.