There are various ways to add members to a group.
Before adding members to a group, create the group. If help is needed with creating a group, please review this article.
Members Tab
Users will need Full Write Groups permissions to perform this function.
First, choose the appropriate group via Groups in the left-hand menu. Next, scroll over to the Members tab. Then select + Add New. This option only allows adding one member at a time; however, multiple people can be added by choosing Keep open and add another. Save or Cancel when finished adding members.
Group Registration
To add members to a group based on a form, first create a group registration form. If help is needed in building the form, please review this article.
Next, add the form as the group registration form. If help is needed in attaching the form, please review this article.
Form Automation
Users will need Full Write Forms permission to complete this task.
Navigate to the group registration form. Under the Settings > Automations tab of this form select Add Automation. The Type should be Group, and then enter and select the name of the group. Note: This will automatically add the individuals who fill out this form to the group selected.
Mass Change within the People Query Builder
This article explains how to add people in bulk with a mass change.