Hello @NaomiWillcox the groups are dedicated to discussions and questions within a certain specialised area. Its a good idea to join any groups relating to your research needs such as the countries you research records in, or topics of interest. Within these groups you can contribute to posts or ask questions yourself.
Hope this clears it up a little 😊0
Groups in Indexing are different. Usually they would be for groups indexing a specific set or record collection - or for administrative organization of people contributing individual indexing effort to the group total. The Church of Jesus Christ of Latter-day Saints - which sponsors FamilySearch - has groups for each organizational area of the church. These are administrative type groups.
If you are working on indexing records not as part of an organization - you won't need to worry about joining a group.3