This is one of those frustrating things that you just have to do once or twice to know how to do it.
If you look at the profile of the gasket, you can see the correct orientation. The rope is on the insided of the cab. The lock is outside and zipped after you get the glass in.
Important is gasket prep befor you try to install the pane. It has to be snug around the perimeter and cut to length to have a good butt joint at the center bottom of the window. If it's not snug around the edge you'll have a gap at the joint. If so, black RTV and next time you'll do it right.
The gasket needs to be clean clean clean, and I like to use wd40 for lube, but it's messy and takes a while to clean the glass when you're done.
You have to try and work the pane into one corner first, then a side, then on around, and you have to gently push the glass toward the corner you started, and then the corner and side. For a back window, you might need a helper in the cab to help you push and keep you from pushing to far in and having to start over or buy a new pane.
I use two picks with handles, they're like cotter-key pullers but less angled. Dang pricey Snap-on stuff. When one corner and side is started, gently use tools to pull the rubber up and around the edge of the glass, working your way around.
An auto glass installer would probably save you some aggravation here, just something to think about. It's easier to show than tell.
Good Luck