GROGGS was based on top of a local messaging system called the CMS (Cambridge Message System), and consisted of a number of 'items', each with a unique itemid (consisting of an upper-case letter followed by seven numbers), and each limited to around 6K in length. Discussions that went on longer than this used to 'continue' into new items.
Each item had a subject, ranging from the sublime to the silly (or, some would say, the silly to the very silly), an item identifier (a letter followed by 7 numbers, which identified the item to the GROGGS commands), and often contained such illuminating responses as 'you're raving, pal', or 'CRB11 is -23'.
In order to ensure fair play, GROGGS has a group of editors (contactable at email@example.com), who oversee the contents of GROGGS, and edit anything that they think contravenes the GROGGS rules. They can also ban people from GROGGS.
Since the demise of PHOENIX, groggs exists in two incarnations - the WWW version (WebGROGGS) at http://mamba.ast.cam.ac.uk/groggs/, and a version running over RGTP (Reverse Gossip Transfer Protocol).
WrenGROGGS is just one of a number of packages that allow you to read from, reply to, or (if you're an editor) edit RGTP GROGGS. RGTP GROGGS is the 'official' successor to PHOENIX GROGGS. Anyone is allowed to read RGTP GROGGS, but in order to reply to it you must register with the editors, and obtain a shared secret. WrenGROGGS can do this for you via the gregister command.
You will then recieve email telling you what your shared secret is. You should use something like WrenGROGGS's grogprofile command to enter your shared secret. It will then be stored in a file in your filespace, and RGTP GROGGS clients will be able to use it to allow you to reply to GROGGS.