When someone visits your site, HubSpot drops a tracking cookie on their browser to identify them as a unique visitor. If you fill out a form multiple times on the same browser, the submissions will be deduplicated based on the tracking cookie and will be merged as one contact record unless you have disabled cookie tracking on your form.
To see raw form submissions, navigate to Contacts > Forms. Click the number in the Submissions column. This will show you all unique submissions on that form. Click on the contact's name to navigate to their contact record. If the contact record has a different name and information than the form submission itself, the record has probably been deduplicated with other submissions.
The best way to manually add several contacts to HubSpot at once is with an import. This will prevent deduplication issues.