This is very user friendly Firefox, directgov on redundancy. There are links on the page telling you about selection, pay and other entitlements, have a browse through. It will hopefully answer some of your questions or at least clarify a few points and give you a basis to work out exactly what you need to ask.
In terms of what you need to get from the meeting, I would expect the following to be covered as a basic -
-How the selection process was conducted, why you were selected. As you can see from the directgov link, often there are several criteria used, sometimes with 'points' systems.
-When your employment will finish.
-Pay arrangements, redundancy pay, notice pay if any.
-References - if there are lots of people being made redundant they will probably have worked out how references will be done, this is obviously when you make sure your current job is on record rather than your previous one. Your manager will hopefully have at least some input into your reference so that's obviously good.
-Any support available to you - time off for interviews, career counselling, other support.
Hope that helps a bit, sorry you are going through this, but hopefully after the meeting the sense of the unknown will reduce slightly and will enable you to work out your next steps.