You can use multiple Google Accounts and Microsoft Exchange ActiveSync accounts on your device. You may also be able to add other kinds of accounts, depending on your apps. Some you can add in the Accounts & Sync screen, as described here. Others you add using an app that works with those kinds of accounts. For example, you can add IMAP and POP3 email accounts with the Email app.
To view the Accounts & sync settings screen described here:
Add an account
To add some accounts, you may need to obtain details from system administrator about the service to which the account connects. For example, you may need to know the account's domain or server address.
Depending on the kind of account, you may be asked to configure what kinds of data you want to sync, name the account, and other details.
When you're finished, the account is added to the list in Accounts & sync. Depending how you configured the account, email, contacts, and other information start syncing to your device.
Remove an account
You can remove an account to delete it and all information associated with it from your device, including email, contacts, settings, and so on.