How can I set permissions (or views?) so that only certain groups can see certain things? For example I have four groups and four document libraries. I want group A to see only group A's document library - B for B ect.
You can easily set individual permissions for each document library or folder. Just go to your header ribbon and click on
Settings > Shared With or pick on
Settings > Library Settings
and it will provide additional directions on who you want to share the folder with. You can remove permissions from other parties with access to the site too under advanced settings after you pick "Shared With" as well.