Go into the directory with all the files created by BOINC (in Debian: /var/lib/boinc-client)

Use the boinccmd command to attach to the manager

boinccmd --join_acct_mgr [URL] [name] [passwd]

And for (boincstats) bam the url is bam.boincstats.com

Hint in the BOINC directory there is a file called stdoute.log – this is a log so tailing this file while doing this might be a good idea 😉