Mucus plug?

Cortney
Hi all, 
This is probably a gross question. I'm a first time preggo and I'm 35 weeks. I just started having a small amount of spotting here and here. I've heard once that starts that it won't be extremely long till you lose your mucus plug, but what does that mean? Will you know when you lose it? I'm just trying to prepare if these are signs of early labor?