Hi
my boss asked me to build a lab in my office so I can practice and learn different VMware products. can you help me on deciding what servers should I buy? I'm newly graduate and I don't understand much about servers and their specs, i'll be installing the server in my office so it shouldn't be loud, also do I need other hardware like routers and switches?
thanks. in advance 
First find out if the company has any arrangements with HP, Dell, or Lenovo for servers (or even desktops/laptops) already. Since you can often obtain deeper discounts that way. Or if there's a specific VAR that's used for the server purchasing.
Once that's done, you'll need to know what the budget limits are for both the hardware AND software side (VMware vSphere licensing).
For a home lab, you need to decide if you're going to go with tower or rack mount servers. If rack, then one or two U servers. Towers are typically easier since they don't require (or desire) any additional hardware and such.
Decide how many hosts you're going to get. I would do at least two hosts with current generation Intel Xeon processors inside. I would also go with a decent memory amount per host. Figure out how many VMs you expect to run, how much RAM those will consume (factor worst case) and then at least double that per host. Such as if you can only see needing to consume 32GB of RAM per host, make sure you get at least 64GB per host. Even if you're only going to run a handful of VMs (at the start at least).
Assuming the OS licenses will be provided by work, so I wouldn't worry about that (let them deal with it).
I would also go for some kind of shared storage array. There are PLENTY of options out there for all budget levels. Look at simplynas.com for a good range of choices.
Don't forget about network infrastructure/hardware as well. if you're doing testing or work, I would request something that will give parity to the work environment.
BTW, for the VMware licensing, you'll want to match the edition in use in the office. That way you have the same features available to you. It would suck to have a more limited version in the lab, compared with what this is supposed to be testing for.
For reference, at my last company, I designed a three host configuration with mid-level processors (Dell R720 hosts with E4-2640 v3 processors) and 128GB RAM, with an EqualLogic PS6210X array (2.5" 900GB drives), single 48 port 10Gb switch. Enterprise Plus for vSphere and a Standard vCenter Server license. Total came to about $85-90k by the time it was all done. That was with the switch barely populated (prices have come down there). I also had a internally provided 1Gb switch for things like host management, vMotion and other admin functions (including the admin VMs and SAN management network). Depending on how you build things out, and if you can get the approval, you could probably go with a smaller 10Gb switch. I would still use one there, along with 10Gb CNA cards in the hosts, especially for SAN and VM traffic. Hell, I'd even do it for the vMotion traffic now. But, in a lab, you COULD get away with multiple 1Gb connections. Just get at least a couple of quad port cards (and enough ports on the switch).
IMO, with the little information you provided, there are no 'simple' answers. The old adage of "it depends" rings very true in your case. 