When initially writing or modifying code it only exists in your browser. The new experience uses your browser's localStorage to hold onto changes, thus reducing the risk of losing in-development work, but it is still important to save your work. When saving a file it will create a new immutable version. Once saved, your code is stored on the cloud instance and available to other team members.
Saving can be accomplished with either a manual press of the green Save button or using the CMD/CTRL + S key command. 03-save-button-with-context.png Mac systems use the CMD (Command) key while Windows and Unix systems use the CTRL (Control) key.
If you are working on a file and have not saved it you will see a white dot on the file tab to indicate it has changes which are not persisted.
Once you've made an unsaved change or if a team member has changed the code the file will then be out of sync. This is indicated by an orange dot on the file tab.
Out-of-sync files need to be "diffed" in order to determine which version of the code should be chosen and saved.