The word rest has several related meanings:

1. To stop working or moving and relax your body and mind. After running around the playground all recess, you need to rest for a few minutes. Athletes rest between games to let their muscles recover. Your brain needs rest too: that's why sleep matters so much. When you tell someone to “get some rest,” you're encouraging them to take time to recharge.
2. The remainder or what's left over. If you eat three cookies and leave two in the jar, those two are the rest. When a teacher says “the rest of you may go to lunch,” she means everyone except the people already mentioned. You might finish half your homework before dinner and save the rest for afterward.
3. To place something down so it's supported. You might rest your head on a pillow or rest your elbows on the table. A painting rests on an easel. When something rests on something else, it sits there, supported and stable.