The lever on the left is the magazine lock. It allows you to lock the magazine, cycle the bolt to remove the shell from the chamber, and still have rounds in the magazine. When I duck hunted a lot, when getting into the boat, I would lock the magazine, remove the round from the chamber by cycling the bolt, press the bolt release to close the action, flip the magazine lock lever back and then have rounds ready to chamber by simply cycling the bolt. It really is a nice way to have the gun "semi" ready but safe since no round is in the chamber.
Some models of the A5 require you to press the bolt release in order to load the gun. After a while it becomes second nature and you don't even realize you are doing it. I hunted with Remington Model 11's and Browning A5's for many, many years and they worked the same. Use it a lot and you will love it. Anything you need to know about Browning A5's can be answered at Shotgunworld.com • View forum - Browning Shotguns
. There are some real A5 experts on that forum.