Groups in Touchworks are found in TWAdmin under the Group Admin VTB What defines a group is not a simple answer. Groups can be whatever they need to be. They are entities that have something in common with regard to the Touchworks Charge module. They are often simply defined by specialty, but sometimes are defined at a more refined level.
If we defined a group as OBGYN. We would build subgroups for diagnoses, procedures, modifiers, etc. for OBGYN. As we are building the sub-groups they can be assigned to multiple groups. For example we might create a sub-group for visit charges and assign it to a family practice, internal medicine, and pediatric group.
You could alternatively or additionally have a group called "Practice A OBGYN" to have a more fine tuned list in the group. The more refined the lists are determines the amount of maintenance for code changes and other items that might come up.