Since you are referring to key servers, I'm guessing that you are talking about OpenPGP here. Note however, that there is at least one more widely used email encryption scheme, namely S/MIME, but it doesn't use key servers, but relies on trusted third parties (Certificate Authorities, CAs).
On the OpenPGP side of things there are many different implementations. These days GnuPG is probably the best known one (at least on Unix platforms).
To upload your key to a key server you have to do the following:
1.) Find out your key ID:
gpg --search firstname.lastname@example.org
The output will contain your key ID, which will look something like this:
2.) Upload the key to a keyserver (in this case
gpg --keyserver hkp://keys.gnupg.net --send-keys B4B887C3479F3215
Most of the public keyservers are interconnected and will synchronize, so uploading your key to one of them (GnuPG, MIT, etc.) should be enough.
Pro tip: Before uploading your key and hence making it publicly known, you should really get a better understanding of OpenPGP. Some aspects of your key (key expiry, key length, sub keys, etc.) cannot easily be changed later on, so making the right decision now is important. Otherwise you'll end up with a bunch keys, which in general confuses people a lot.