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.
You cannot navigate to the next step until you fill in the current step details.
If you are editing the record (form), you will get the multi-step.