'Member Subscribe' saves each person who fills in the form as a member, as well as sending the entry to the form's board.

In your form's settings, GENERAL › Member Subscribe has the option Yes: Subscribe as Member. Choose it to save every person who submits the form as a member.

Member Groups, just below, names the group or groups those members join. Member Groups decide who can see members-only pages (Page Settings › Member Group).

Choose the other option if you only want the entry and not a member.

Press SAVE & EXIT, send a test entry, and check that the person appears in your Members list.