When you get to the neck opening, just drop the strand you're working with and use a new strand to bind off the 4 stitches. Don't worry about how to attach it. Just start using it. The fact that the first 4 stitches are bound off will secure it.
The 'bottom' stitches in this case are the first 5 and last 5 stitches on your needles.
At this point, my suggestion is to start the sweater. Things such as bottom and neck stitches become so much more obvious when they're right in front of you. It's good to read a pattern before hand, but if you try to understand exactly what's happening, it gets confusing.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry