So the first thing you will need to do is create a case if you don't already have one.

Opening new Discovery Accelerator cases

It would be possible to use Research folders, but I want to keep this simple.

Second, you need to run your searches:

Creating and running Discovery Accelerator searches

You will probably be best to do two searches, one with your user in the From field and one for the user in the To field.

After you run and accept the search then you can export it to a PST.

Performing an export or production run

I hope that helps but you need to tell your management to get you some training.  The forums are great but using DA requires complete training that you relly can't get from a forum. You really don't want to screw something up when dealing with legal issues!

HTH,