Assigning different user names on multiple pc?

Hi,

Can someone PLEASE help me how to set up or assign usernames and password on each pc for students.

I want to set up a pc where each student can come and enter their username and password and log on to the system. Also is it possible to set up if a student wants to access their files or folders on a different pc, having them just to type their username and password on that pc?

Otherwise, what I am trying to achieve is how to set up a username and password on a pc so that each student can enter their different username/password and access their school files/folders. For example, one student finish using the A.Computer - then another student comes on and enter his/her username and password access their files, and so on on the A.Computer

The school computer room has only 12 pc. 1 Router to access the internet.

This is a Primary school (computer room) that I am trying to help.

Can somebody walk me with the step...

Many thanks.