You can create a group on both the web version as well as mobile app:
Click the menu, then go to "Groups":
Next, hit "Create New Group"
Next, give your group a name, select the category, add a good description and set whether you want the group to be Public or Private. You can also add a group cover photo as well:
Bottom right, click the 3 lines "More"
Next click "Groups"
At the bottom right click the + button
Add a Group Cover photo, group name, category, description and set whether the group is Public or Private.