To progress in a restaurant and unlock more levels to play, you need to collect “Keys” that are used to open the Gift Box.
You can see how many keys you need under the Gift Box or when you tap it.
These keys can be seen and collected by finishing either the 1st, 2nd, or 3rd star of the level.
Once you have collected all the required keys, click on Gift Box to open it, then the next set of levels will be unlocked.
Happy cooking!