This is enabled under Settings -> Groups -> Group Finder. At the top of the page there is a simple Yes/No option.
Once enabled you can make further choices that pertain to which groups can appear, and what options users can use to filter groups in the member area.
They’ll see each section has a “Filtering” and “Restriction” option.
“Filtering” means if users can filter groups based on this information on the front end or not. For example “Can the user choose to only look at groups in Group Categories they want to look at” or “Can the user find a group based on demographics that are relevant to them”
“Restrictions” allows the church to limit what groups appear. So they might want to restrict to only display groups assigned to the Adults demographic and in the “Small Groups” category. It’s entirely up to the church.
For existing Churches who are enabling this, I’d also recommend adding “Group Finder” to their navigation menu under Settings -> Layouts, as discussed further in this article. New accounts won’t need to do this, but existing churches who’ve customized their menu in the past will need to. This allows people to actually find the page in the Member area.