Record owners field allows you to assign one or more record owners. To add it to your form, open the Form builder and go to the "Advanced" tab:

Record owners field on the form:

Adding a record, you can specify one or more record owners. To add one more owner use the plus (+) icon.

To remove an owner, use the trash can icon.

All Team and Customer Portals users (all apps portals), those who have access to the current table, will be available in this field in the Records menu or in the Form Widget.

Using the form with the Record Owners field in the Portal, only this portal users will be available.

You can use "By default the currently logged in user is selected" option. In this case, the portal user will see his login in the field by default. Also, if you need to have only one record owner, you can activate the corresponding option on the field editig page:

Also, you can exclude the current portal user from the list:

In this case, the user will remain the record owner, but there will be no need to mark him from the list every time.

The users list can be represented as checkboxes:

To do this, you need to activate the "Show as checkboxes" option:

Using the Record owners field will greatly facilitate the Portal and Team users access rights managing.

The field can be used in Subforms. For example, there is a table "To do list" and a subform "Tasks". The portal administrator can assign responsible persons to perform tasks.

The "Tasks" table has access to own records only for portal users. Therefore, when the user enters the portal, he will see his tasks only:

In the Records menu you can use the "Added by" control to filter records by owner.

And save the result to a report.

Don't forget that you can change record owner using the "Actions" menu at any time.

Read also: How to filter records by user