Wago ???

How do they work?

They work well.

They work very well. makes life fairly simple.

A lot simpler than wire nut

In words:
Raising the cam lever compresses the spring contact. A stripped wire is inserted into the gap. Snapping the lever down allows the spring contact to rise and "choke" the wire in place.

Yeah they're pretty straight forward. The only thing that took me a couple seconds the first time was, it is much harder to open a lever than I anticipated, you've gotta put some force on them. I was worried I was going to break it.

Do they work on just one side? (+) (-)

These are modern wire nuts--all inserted wires are connected together.

The most common ones don't have a lever, just angled blades that kinda grab the wire. Think of it just as a wire nut. Not polarized. Pain in the ass on stranded wires, you push a tiny little screwdriver into the release hole to move the blade off the wire to remove. They come loose often. Very often. Their reason for existing is because they are cheap and fast. Wires larger than 14ga don't play well with them and come loose much easier.

If you've ever tried to splice 3 or 4 12ga wires together in a box with one of them, you wouldn't be praising them.