The main thing with servers is if they are networked and you are dealing with drives or "volumes" on other machines or NAS or other network mounted storage. You also get load leveling with some machines like databases on one machine, email server on another and so on. If its a windows machine you have to deal withe Active Directory and all of it's nightmares. But these are all O/S related issues, not hardware.
Sometimes programs you are familiar with like disk cloners/duplicators, anti-virus software, and so on will have a server version as opposed to a single-user version. It's not a big deal but sometimes a little more reading on new functions. It's just like anything else in our business, learn by using a client as a guinea pig and as you become more confident, call yourself a specialist.
Do you know what kind of servers you are looking to get involved with ?. Start slow, no harm in telling someone you do not work with certain things as you slowly immerse yourself into all of this.