I volunteer with American Red Cross blood drives so I can really only speak on that experience.
The process isn't too different than with normal whole blood donations. The requirements aren't too different either. Be healthy, over 110 pounds and over 17. For more specific requirements please check
here.
If you go through red cross or basically any blood bank, they will give you snacks and juice/water at the end to up your blood sugar and make sure there are no complications. It is a good thing to have eaten and to be hydrated when you go in. Plasma generally takes about an hour and fifteen minutes to an hour and a half. Whole blood typically takes an hour. A lot of it is going through medical history. The medical history is completely confidential and is only asked to make sure they can use your blood.