Does it find all the contacts and automatically add them or can you choose which ones you want to add?
No, it doesn’t add them automatically. When Facebook first came out, it used to put check marks next to all of your contacts and it would send invites to all of your friends with a single click. However, it’s not like that anymore. If you use the email finder, it will find all of your contacts that already have a Facebook account. You then need to put a check mark next to everyone you want to send a friend request to. You still need to click the "Add as Friends" button before friend requests are sent out. It doesn’t do it automatically.
You will also see another screen with all of your email contacts who don’t have a Facebook account. That screen has check marks next to all of your contacts, but you still need to click the "Invite to Join" button before sending invites out. It doesn’t do it automatically.