Basically these critters point out from your windshield, & record everything you see from the drivers seat. If a car ahead suckers you into tailending it (the old insurance scam), and claims it was your fault...well, it can't! https://www.lifewire.com/best-dash-cams-to-buy-4062264
It seems there are different laws in each state, much easier over here A dash cam has been a very good addition and does stand up as evidence
To bad each state in US can't get on same page with laws and policies...would make life easier for many I think.
Forgot to mention that motorcyclists and bicyclists got their own version that attaches to the helmet or handlebar!
I use one that attaches to the windscreen. They are available quite reasonably in most filling stations. As is the required SD card for storage. It can, for some reason, be quite tempting to watch the screen rather than the road ahead! Fortunately my screen can be folded away.