Registering pre keys with server in signal protocol

I was recently going through documentation of signal protocol. https://github.com/signalapp/libsignal-protocol-javascript. In the documentation after they generate the pre key bundles and other things they say “// Register preKeys and signedPreKey with the server”. But there is no mention of how to do that. Apart from this can anyone please help me with how to know a users recipient id to decrypt his message. Also are the keys permanent or they disappear on closure of browser.