how to set a bed and the rules around it

bed

A bed is a block (actually two blocks) that has two main functions: They allow the player to sleep through the night and skip to the next dawn, and they reset the player's spawn point to within a few blocks of the bed. In multiplayer, all online players in the overworld must lay in a bed for the world to skip to dawn.

If a player's bed is destroyed or the bed is surrounded by solid blocks and the player dies when the player had set his spawnpoint there, a message is displayed saying Your home bed was missing or obstructed, and the player will respawn at the original spawn point. With this in mind, the player should know how to navigate to their base with the bed from the original spawn point, or keep their base near the original spawn point.

http://minecraft.gamepedia.com/Bed