Good morning brian and welcome to Stovebolt.com.
As Bruce says, that's the parking brake handle -- pull it back and it's engaged. Squeeze the handle (to release it) and let it go forward, and you're on your way.
1st gear on these trucks is a granny gear -- when the truck is empty, or you're starting out on level ground, you can skip it and go to 2nd gear. Just drive it and the truck will teach you when to use first

First gear also has no synchronizer so you will have to double clutch it to use it (you can start in 1st and upshift to second on the fly, but once you leave 1st, there's no going back unless you stop first or double clutch.
Don't be afraid to try it -- you're going to clash gears -- that's okay for awhile. It's a tough tranny and it will be a good teacher

And before you know it, the guys will have you driving a Road Ranger.
Have fun and welcome to the hobby!
Let's see some pictures of the truck.
John