Crank sliding horizontally through the bottom bracket
You need a large allen key, often an 8mm to tighten that centre bolt right down.

It'll pull the crank arm onto the spindle and secure it.

The LH-FSA-AL ring is the self extracting bolt, the internal hex bolt pushes on the back of it to pull the crank off without extra tools. That has a left hand thread so that it doesn't unscrew as the internal bolt unscrews. It only really needs to be tight enough to stop it from coming out, finger tight probably isn't enough though.

You need a pin spanner for this which is a pretty specialised tool, I've certainly never had need to buy one, so you might want to pop down your LBS and ask them to tighten it up.