I just downloaded Inkscape yesterday [mainly for the purpose of doing lineart] and have spent quite a while trying to figure it out. I've had a few questions and have managed to figure them out myself, but there's one I am completely lost on.
[By the way, I have read the FAQ and the manual! Although there's a chance I missed something that could have helped. If so, please just tell me politely.]

Say I have a sketch on the bottom layer. I make a new layer with the lineart on top, and I want to erase or get rid of the sketch lines underneath. How would I do this? I tried using the calligraphy tool [ ] to erase, but that doesn't work. Can I delete the bottom layer?? is there some other way to erase the sketch lines?

Thank you for your help.

Go to the layer with the sketch lines, on the bottom you'll see an icon of an eye and next to it an icon of a lock. The lock means it that the layer it's used on will be basically paralyzed and you cannot select or edit it (could be useful), and the eye means to put the opacity to 0% which is what you're looking for.

Oh, alright. Thank you!!

Welcome! Glad your generally finding your way round inkscape ok, and have some brownie points for trying the manual first

Bonnie wrote:Can I delete the bottom layer?? is there some other way to erase the sketch lines?

If you want to actually delete it then make it current, and do Layer>Delete current layer. That will get rid of the layer and everything on it.
You can also do it with the - icon in the layers dialog (shift+ctrl+L)

If you just want to hide them then the eye icon that Jackovich mentioned is the way to go.