Don't look at the needle and you should be OK.
You are going to feel a little *****.
No worse than donating blood. I donated plasma for years and it is a very rewarding way to contribute.
The needle is bigger but don't let that put you off - I honesty did not feel that any more than a normal blood donation.
It does take a while though so be prepared to be there an hour or so.
It pinches a little like giving blood but it takes longer. Makes sure you are very hydrated.
They ***** your finger for a quick test, then they stick a needle in your arm and leave it there for about 1/2 hour. The people who stick the needle in your arm are trained like CPR ... a couple classes and a small fee to get 'certified' If you do go then ask for the phlebotomist who has worked there the longest.