There's documentation everywhere about nightly, and the software I am trying to use says it requires nightly, but for the life of me I can't find a straight explanation of how to use nightly?
Note I have rustc and cargo but not Rustup as it does not run on Alpine Linux.
We don't currently build distributions for x86_64-unknown-linux-musl, so you'll have to see if whoever is creating the distribution you're using now builds nightlies as well.