Co-broke means the listing agent shares part of the commission with the agent who brings the buyer. It makes every member a possible seller of your listing.
When you add a listing, state the co-broke offer (amount or percentage).
A buyer's agent can accept your offer, or propose and counter-offer, inside the listing conversation in Messages.
Every step (proposal, counter-offer, acceptance) is recorded and emailed to both agents. See all agreements in Messages → Co-broke agreements.
You can also refer a client to another agent with a referral fee (20%, 25%, 30% or your own terms) in Messages → Referrals.