All member groupss should be able to use the gallery. Just go to My Controls > Invision Gallery > Your Album
and you should be in your Album Manager and input your Album Name and description. You also can make it private or public by ticking on the box available there.
Private gallery only can be viewed by you, mods and admins. Every members can view your public gallery.
You can use it to host whatever images you want, within reason - no gore or porn though (IMG:style_emoticons/default/smile.gif
New member groups currently have 5MB allocated space to host, Members and CL Members has 10MB, and you can create unlimited albums within your allocated space (at least for now) but don't spam the gallery though. and I hope you enjoy using this new feature.