How are domain zone files created on secondary dns servers?

We're running Bind 8 and we maintain the primary DNS server in house.  In addition to our home domain, we also have 25 or so other domains that we're the primary for.  We're going to be switching ISP's, and the ISP will maintain the secondary DNS servers.  What's the process for these zone files to be created on the secondary servers?  When I add them to the primary I have to create a zone file with the A records and such, and then create any entry in the named.conf file that defines which zone file to use for the domain.

Does someone have to do the same thing on the secondary DNS servers to initially create the zone files?

Or are they created automatically when the zone transfer takes place between the primary and the secondaries?  

l know that to update the zone files you increment the zone file serial number, the secondaries poll, see the serial number has been incremented and then initiate a zone transfer to update the zone files on the secondaries.  Check me if I'm wrong on this point.