I've never personally used these or know anyone who has. However, I have had braces and now wear retainers at night.
If they're anything like the retainers I use (clear see-through plastic) they just slip on over your teeth. I've been wearing mine every night for probably 5ish years now? The only things I can tell you from those though are that if I do forget to wear them a night or 2, then when I do wear them again my teeth usually hurt (very little) the next day. But you get used to using them and it's easy to go to sleep with them in.
As for cleaning I "try" to clean them once a week with (iirc) polydent (denture lol) cleaner that you put the tablets in a cup thing and fill it with water, and then let them sit for a while. But every once in a while I have to actually brush them with my toothbrush. Just remember to brush your teeth before putting them in!
I would DEFINITELY talk to you dentist about them though, they usually know what's best for your mouth or at least stuff to try~