What is the difference between scripts and localscripts?

Scripts run on the server, so if you want everyone to see a block move, you would use a script. Scripts can be used just about anywhere

Localscript only run on the client, and only work in the Startpack/Backpack and StarterGui/PlayerGui. These are mainly used with GUI's because when somebody clicks a button in their gui you don't want the result to happen to everyone. Local scripts are also used with cameras.