When you create a Google form, only you will be able to make changes to the form, by adding questions or changing settings. You can share a form with everyone in your organisation, or with specific people only, allowing others to contribute to the form and make changes. These sharing options control access to editing the form only - who can fill in the form is controlled using the options along the top of the form. 

Once you have created a form, it can be shared as follows:

If you have sent an email notification, the invitee will receive a message in their Inbox, which will contain a link to the shared form. 

If a colleague edits the form, you will be able to see which question they are working on. 

All changes will be saved to the form automatically.