Server vs Client Side Scripts and Beginner Issues

Sorry if these questions have been asked before but I was on google for a bit and got nothing.

My first question is quite simple why is there Client and Server Sided Scripts, and when would I use each one?

My second one is where would I get some good tutorials for entity scripting? Most links to tutorials I found are either more complex things that I have yet to be skilled enough to try or they are dead links that lead to no where.

1:

Client side scripting is for the clients, or if you will, the players. This will be for things such as the heads up display, or menus. And Server side scripting is for everything you don’t want the client to handle, such as profile saving and loading, etc. When you use them is up to you, there is never just 1 way of completing something.

2:

The Lua PIL is a good start. After reading that just start reading through the wiki.

Hope this helps.