Ghost notes

Hello everybody.

I'm wondering about how ghost notes are played on the mandolin, especially the ones that are noted on an open string as the tab would show it. I'm not even sure if it's a ghost note actually, but they're in parenthesis so I'm thinking they're ghost notes. This is bluegrass music I'm talking about.

I'm learning this instrument on my own, since the nearest mandolin teacher is miles from here. So the learning curve is kinda tight.
Thanks.