How can I have someone eneter their email to have access to a link?

There are a few ways you can show a link after portions or the whole form has been filled.  You could show the link in the thank you page:

http://www.jotform.com/help/211-Setting-Up-the-Thank-You-Page

You could conditionally show the link in a field in the form when the previous fields are filled in:

http://www.jotform.com/help/57-Smart-Forms-Using-Conditional-Logic

Or you could add the link to your autoresponder email so the users receive the link via email once the form is completed:

http://www.jotform.com/help/26-Creating-a-Form-Autoresponder