The first unnamed parameter specifies the operator of the bot.
2, 3
The second and third unnamed parameters can be used to specify co-operators of the bot, if required.
site
The two letter code for those operators that do not have an account on the English language Wikibooks (though having a local account is strongly recommended).
status
active (without flag), approved (with flag), inactive (but approved), trial, unapproved, or globalbot
awb
yes (if this bot uses AWB), or omit (if it doesn't).
codebase
The name of the code (programming or scripting language) used to create the bot (e.g., pyWikibot, perlWikibot, ...)
brfa
Optional if specified, overrides the name of the request for approval. If not specified, defaults to {{BASEPAGENAME}}