Welcome!
To newcomers, BES stands for BlackBerry Enterprise Server. Usually, this is of interest to businesses rather than individuals/prosumers.
Individual users who need BES Hosting or just want push email without the BES enhancements, you will want to see my
BlackBerry FAQs
If you are a business who is new to BES: If your business is running Microsoft Exchange, and you need some solution that puts your corporate email onto corporate BlackBerries, you will want to read
Blackberry Enterprise Server for Microsoft Exchange. There's also a
Lotus Domino version of BES, as well as an upcoming
Novell Groupwise version.