Always try option one first as you can do this and don't rely on the end user to input the details but this sometimes is not possible (Phone model dependant).
Go to the internet on your PC, go to one of these websites below depending on network. If the users network is not provided just search BIS (network) in Google.
If the blackberry has already been setup they should have a username and password, get them to call the network if they don't know it (it will save you a lot of time). Once you're logged in you can configure and edit any POP/Exchange accounts using the general settings. Note the mailbox name is the email address. If you don’t get this right it will not work!
To set up a new/unregistered phone you will need to two pieces of info, the device PIN & IMEI number. The website will give you some info on finding these, Google if this doesn't work as there’s more than one way. Failing that it’s under the battery of the phone or on the box. Create them a new account and let them know the username and password. Tell them to look after this information as we have no way of keeping track of this (unless you want to).
Again note, the mailbox name is the email address. If you don’t get this right it will not work!