The Data-Link module can be used in two different ways.
What is an online panel and why should I "Hydrate" it?
You can use surveys to collect email addresses and add them to an online panel. Using the Online Panel Management interface, you can then send automated and "intelligent" email campaigns to the members in your online panel.
How do I Pre-Populate Data? For example I already have the First Name and Last Name and I'd like them to verify and update that?
Data Prepopulation can be done when you use the Email/List Management interface to send the emails out. With the Email/List Management interface, you can upload upto 4 "Custom Variables" -- These can be any arbitrary data that is linked to that person (email address) -- Once you've done that, you can then link each of those custom variables to a single question data element.