There should be metal clips around the front and rear glass attached to very small studs. Place the trim over the clips and push down until it locks. If you look at the back of the trim you should see signs of where the clips locked originally.
If you do not have the clips you can get them from Classic Industries. I bought mine there. Ground Up may have them also. They do install as previously stated. They just push down over the studs on the body of the car around the windshield then the trim snaps down over the top of the clips
Welcome to the forum. Like others have mentioned about the clips sliding over the studs around the window frame in my case I had 2 of the studs broken off and I was able to use a long drill bit and drill a hole where the stud was located and used a small sheet metal screw to attach the clip.
They make screw-in studs if you don't have access to a stud welder.
Or screws or even pop rivets to hold the clips.
If you're missing the clips... They are easily available from most automotive restoration places.
It really depends upon the level you plan to take the car.
Might be worth taking to a body shop for a quick stud weld job if that's what you're missing.
Look how the trim fits before you snap the first piece in place. Might be a simpler task to slip the ends together first.
(I've never done an early 2nd gen with the small rear window but it's definitely easier on the later wrap-around windows.)
Welcome to NastyZ!
Look around the site, use the search feature and post up some pics!