Was this where we were discussing dashcams recently?
Put one in my car a while ago - an expensive integrated one which looks factory - but I got this cheap one free with something so put it in the small car my kids mainly use.
Took some photos to show that it is fairly straightforward.
The kit came with a cable that plugs into the 12v socket - but that means wires hanging around and I wanted it all hidden.
I bought this kit on Amazon for about $12. It has a thing that just plugs into the fusebox and different ends to fit your camera - I chose this one because the end fit mine without any adaptor - once less thing to have to hide.
Other things I used - screwdrivers, a socket set (not pictured), and trim removal tools which are handy for getting into things - you'd get away with a butterknife if you were careful.
I first tested it to makes sure it works just plugged into the 12v socket - and checked where I wanted to put it. I put it behind the mirror so you really can't see it when driving.
If you pop open your fuse panel (usually there's a hatch near the steering wheel) you'll see something like this. Choose a non-critical fuse - you don't want to plug it into your brakes or something in case it causes a problem. I used one of the 12v power sockets.
The main tricky part is getting the power lead from the fuse panel to the camera - I eventually dropped a piece of string down and then taped it on and pulled it through. Then you can pop the rubber door seal off and just run it up the side there.
Along the top of the window is easy, you can just tuck it into the headliner - and down the pillar is easy too.