networking - How do I map a network in Visio?

I work for a organization which runs several servers mainly used for internet to schools and Exchange on the corporate side.

One of my tasks during my training is to be able to understand the network and how it works.

Now I don't need to understand absolutely everything but I would like to map out the network in Visio to see how it connects together via a visual perspective.

We have 1 core room which holds the main servers and switches for http/mail/voice/storage etc. which are connected to several switches in other "sub" rooms which then connect that section of the building, i.e 1 Hop.

So my task is to be able to track all the connections leading from the main server room going to the sub switch rooms, so we know what connection does what.

Do you guys have any idea of how to get started with this task, how to go about it, etc.

I'm not 100% guru with Servers as I'm just a MA - Technician and will need to learn how the servers interact with switches and how it all comes together.