How can a user share a form with another user?

You can add a user as a collaborator to a specific form. It's a real-time, seamless experience where multiple team members can simultaneously work on the same form. All changes are automatically uploaded so you always edit the most current version.

You may refer to this guide about Form-Collaboration.

Please note that a collaborator has access in viewing and editing the form inside the Form Builder only. They don't have access to the form's Submission page.

If the Form owner would like to also share its submissions page,  he can make the submission page public and set a password, then share that password and link to the collaborators. 

Here is the guide: How-to-Share-Form-s-Submissions-Page