Collect BB-8's Memory Discs to unlock new levels and Memories. Upon reaching a locked Memory level, make sure you have completed ALL the listed requirements to unlock.
If you have met the requirements to unlock a Memory level, you can spend earned Memory Discs to Unlock or the Memory level will unlock itself when the timer reaches zero. If you don't have the required amount of Memory Discs, you can spend Gems to "Unlock Now."
When tapping on a level, the rewards and goals will be displayed. Beating a level will unlock Expert difficulty settings, and allow you to get any Memory Discs that are awarded on Normal or Expert.