Every nanopublication is signed, so you need a key pair. Nanodash makes one for you on your profile page and keeps it with your account, so you can publish from any browser after logging in. If you also publish from the command line, that tool keeps its own key in a file on your computer.

The private half of a key never leaves the place it was made. The public half is published, in your introduction, so that anyone can check your signatures.