How do I delete the emails from my forms mail boxes?

I cannot figure out a way to delete emails from the in boxes for my emails.

In addition, for the free account is there just 100 incoming emails for all time or is it for once a month. That is not quite clear.

I cannot figure out a way to delete emails from the in boxes for my emails.

If you're talking about literal emails that come to your inbox (not JotForm), then deleting them would highly depend on what email client you're using. As a general example, here's how you can delete emails in GMail.

On the other hand, if you're hoping to delete Submissions (not emails), you can do that on the Submissions Page. Just keep in mind that when deleting submissions individually, you will see this warning message (see screenshot below). Please note that deleting submission data is irreversible and will permanently remove it in our servers, including the file uploads on them.

Complete guide: How-to-Delete-Form-Submission-Data 

In addition, for the free account is there just 100 incoming emails for all time or is it for once a month. That is not quite clear.

The 100 limit per month on the Free Plan are submissions (100 monthly submissions). These are not emails per se, but rather Form Submissions. You would get emails for each form submission if and only you have added an Email Notification to your form.

Related guide: Setting-Up-Email-Notifications