I am lost with the Google sync how to!

1. Do I need an outside (down-loadable) app for my phone (ATT Captivate) or is it built in.

During my initial set up of the phone I entered my Gmail info. It was interesting and confusing, when I looked at my contacts for the first time. Wow there were my email address set up in my Gmail account.

That's cool but how did I do that? and when does it change, if I were to add additional contacts?

2. I've read many different site's regarding transfer of info between Gmail and phone, Google even has a Video explaining what it does. They also give a list of the devices capable of utilizing this cool feature.

So I see what was loaded to my phone, through Gmail, but how do I create the reverse? I need to transfer all my contacts that were on my SIM to my Gmail account???

I downloaded an app from the Android market called "Backup to Gmail". I truly don't even know if I needed it, however it didn't transfer my phones contacts to Gmail, or did it? Where would they be. There's a contacts button when your in Gmail and these are the ones the phone added to the contacts on the phone.

Somebody please help a totally confused guy
Thanks, Tomween1