If you have enabled the multi-step Form for the Add/Edit form (records), the portal users will get stepwise form filling. The steps are the section-wise details that are added in the form layout.
Once you fill in the details click on the “Next” button to navigate to the next details. [1]
You cannot navigate to the next step until you fill in the current step details. [2]
If you are editing the record (form), you will get the multi-step.