It's possible to let users select their own group with the 'self-selection' feature. Follow the steps below to enable self-selection.
Go to User Management and select 'Manage groups'.
In the group view the second column shows whether a group is 'selectable' by users.
To change the setting from false to true click edit group under group options (first icon in the third column). Under the second header check the box 'Allow users to select on invite'.
When the setting is set to true this doesn't necessarily mean all users will be able to self-enroll in groups. Self-selection will only be available if the users' invitation allows self-selection. On both single invite and the open invite's you will find a checkbox with the name 'Allow Group Selection'. When this box is checked the user will see all groups that are selectable upon first sign-in.
When this box is checked the user will see all groups that are selectable upon first sign-in. Please find an example below.