Goldengate in help in general is not very user friendly but, a good start is the help command at a ggsci prompt:
For help on a specific command, type
HELP <command> <object>
Example: HELP ADD REPLICAT
This guy has supplemented help at this blog… a truly useful summary of commands – it may not be complete – but it touches on many useful…
http://myoracleproduct.blogspot.com/2014/04/ggsci-command-summary.html
GGSCI command Summary
ggsci> help
Object: Command: SUBDIRS CREATE ER INFO, KILL, LAG, SEND, STATUS, START, STATS, STOP EXTRACT ADD, ALTER, CLEANUP, DELETE, INFO, KILL, LAG, SEND, START, STATS, STATUS, STOP EXTTRAIL ADD, ALTER, DELETE, INFO GGSEVT VIEW MANAGER INFO, REFRESH, SEND, START, STOP, STATUS MARKER INFO PARAMS EDIT, VIEW REPLICAT ADD, ALTER, CLEANUP, DELETE, INFO, KILL, LAG, SEND, START, STATS, STATUS, STOP REPORT VIEW RMTTRAIL ADD, ALTER, DELETE, INFO TRACETABLE ADD, DELETE, INFO TRANDATA ADD, DELETE, INFO CHECKPOINTTABLE ADD, DELETE, CLEANUP, INFO
Commands without an object:
(Database) DBLOGIN, LIST TABLES, ENCRYPT PASSWORD
(DDL) DUMPDDL
(Miscellaneous) FC, HELP, HISTORY, INFO ALL, OBEY, SET EDITOR,
SHELL, SHOW, VERSIONS, !