The silver things are runners with ball bearings that drawer slides on. The slides that attach to the drawer will snap into these silver runners.

Usually, you just need to align the slides on the drawer with the runners and push. They should snap in. The runners tend to slide around while connecting them. If they slide to the back, it’s ok, they will still connect once you get them lined up and push the drawer into them. If you can reach from underneath, you can hold the runner in place while attaching the drawer. Do one side at a time.

If you’re struggling to get it to connect, I recommend removing the slide from the side of the drawer and seeing if you can get a single slide to attach to the runner. It will click when it attaches. By doing just one, you might have an easier time seeing how it connects.

Once you figure it out, you’ll need to disconnect it. There should be a little plastic lever that you hold down (or up, depending on the side) while you pull out the slide. Put it back on the drawer and see if you can connect it once it’s back on the drawer.

They are a little complicated, but once you see how it goes together, it should make sense. If what I said is still confusing or if you are still struggling, reply and I’ll see if I can get some pictures to explain it better.