If you’ve donated blood before then you should be a pro with plasma!
Personally, it hasn’t hurt, but the doctors say that it’s different with which person. Basically, they put a needle in your arm and take the blood, then a machine separates the plasma, mixes your blood with saline water, and injects your blood back to you (It isn’t as gross as it sounds :p ). The process shouldn’t take more than 45m to an hour.
I’d recommend that you don’t do any heave exercises afterwards, to help your body recover better and replace what you’ve giving away.
Again, if you have more questions, feel free to just ask! :)