Hmm well a mouse will be easier than a rat to keep but I only know of rats so keep that in mind but the info should still be accurate.
You can either use a glass or plastic aquarium or a steel cage. Glass can get hot and ammonia builds up faster than it would do in a steel cage which is what I used. You want a decent fitting roof for it too cause they can really jump and being a cage, it's easier to attach things like the water bottle and any toys but they climb on the walls pretty well so has to be able to keep em from escaping obviously.
You can fill the cage with either sawdust or cat litter, something like that just don't use something like a mesh floor, you can imagine them getting their feet stuck. Food-wise is basically just grains, they like sunflower seeds and maybe every now and then some vegetables, I put them in really tiny clay pot.
There's all sorts of things you can add to the cage if it's a decent size, I had a fake hollow log and it was winter at the time so I would drop in shredded tissues and my rat would make itself a bunker, I had that and a little mouse wheel.
You gotta get used to cleaning the cage too, like once a month I think you change all the cat litter floor. It may take a while for the mouse to get used to its new environment so just get it used to the sound of your voice, shouldn't be a problem, goodluck.
