Don't need the stone, but it's helpful for moving from one camp to another. Anyway, group leader right clicks on an adventure recruiter, then select the options and request an adventure. If you don't like the one offered you can decline and wait several minutes to get another offered back from a new request. When you get one you like, accept and you're on your way to the instance.
Things to note: There's a 10 level group member span limit. Only the group leader can request missions. The 90min time limit starts as soon as the first person enters the instance. I don't remember what happens if you don't make it, but you only have 30mins from requesting a mission to get someone to zone into the instance.
AFAIK, there's no way to cancel an accepted mission, other than waiting 30+ min without zoning into the instance.
Here's a link to a thread that's an LDoN Overview:
https://everquest.allakhazam.com/fcluster/gotopost.pl?mid=127563779851314685 Yther Ore.