So, basically you go to a house, in front of the house there is a marker. If it is green it's for sale, otherwise it'll be blue, in that case, someone already bought the house. There, you can save your inventory , weapons, medic-kits (i guess). You can also spawn your onw car by the house, if you have one, of course.
If you donate and buy "tokens" (
https://forum.igcrpg.net/index.php?topic=175.01), you can have plenty more features regarding your house, and other things aswell.
I think its pretty much it..
Sorry if I didnt fill you in completly. Reply for more doubts.