When you serve tables, you collect Gems in the Tip Jar.
You can buy the Tip Jar whenever you want however, the more Gems the Jar contains, the better the deal!
Keep in mind: You won't be able to collect more tip Gems once the Tip Jar is full.
Once you purchase the Tip Jar it will start to fill up again and when it is full you will be able to buy to again.

Check Out the Tutorial HERE