Membership in the BFRO is by invitation only. Invitations happen after a person meets enough existing BFRO members who can recommend an invitation.
You can meet BFRO members by attending BFRO expeditions.
The BFRO hosts expeditions in the U.S. and Canada which are open to non-members. These expeditions usually last four days -- Thursday to Sunday. You can participate if you're able to camp in the woods for a few days. See the locations and dates on the 2019 Expeditions schedule page. On that page you will also find a link to the Expedition FAQ page with registration instructions and more details about these trips.