Network Design

I have a question about how to organize and setup a network so that it is isolated.

I am new to the IT world with no experience or real training (as of yet). I was hired on at my company to learn on the job and acquire my skills in that fashion.

I am currently in charge of redoing the network in one of our labs because of some recent mis-haps and the buildings network crashing.

My question is how to go about setting up a network so that it is isolated from the rest of the buildings network using a switch. This is a test lab and I need to design the best setup to allow for ease of expansion for any future use.