When creating a new project, they are private and secure by default. The only people who have access are those you explicitly invite to the project.
Projects can be set to Public or Private to Team Members. A Public Project means all Team Members have access to see the projects and add themselves to the project. Private Projects are only seen by the Team Members that are added to the project by the Project Owner.
Enable Slack Notifications allows all notifications to post to a Slack Channel. Slack is a messaging app for teams so if you're not currently using it for daily messaging, disregard this section.
Project Sharing gives Collaborators the ability to join the project without an exclusive invite. This is great for inviting many users without inviting each individual user.
Collaborators already have limited permissions in your project but you can choose to allow or not allow collaborators to download media, invite other collaborators to the project or share media.
When Can Download Media is on, collaborators will have access to download the original files uploaded to the project.
When Can Invite Collaborators is on, existing collaborators can add other collaborators to the project. You will be able to see all collaborators added and also be able to remove collaborators from the project if any were unauthorized. When the option is off, only the Project Owner or other Team Members can add collaborators.
When Can Share Media is on, collaborators can create branded presentations of clips or a group of clips.
Scrolling down on the Project Settings page:
My Email Notifications displays what YOU want to receive in regards to email notifications. When comments are made by anyone other than you, you will receive a New Comment notification. When New Media Uploads are added, you are notified. In conjunction with allowing collaborators to invite other collaborators, you will be notified when a New Person Joins.
Everyone Else's Email Notifications sets the default notification setting for the collaborators. However, if the collaborator visits Project Settings, they can turn on or off any notification setting for just themselves.