Most BBS's should have a copy, or know where to find one. After these are configured, various items about the door itself must be configured. For a game, it may be the number of turns per day, for a credit card system what types of cards are supported, etc. Configure these as you wish. Test the door in local mode, if it is has such an option.
Most doors have a command line switch, or some other way of runing the door in 'local' mode.
The purpose of testing ahead of time before adding it to the BBS is to make sure the the door itself is properly configured. In all cases, check the documentation of the BBS software you have selected for proper configuration. In this case, you need to configure the BBS software, which will usually have a set of configuration options relating to doors. Doors run on BBS's of this type may have problems with memory usage. For this reason, some BBS's have a special option to let you 'minimize' the memory usage.