Serve your customers before their patience runs out. You have to earn enough daily money to pass to the next level (in level 1 is enough to earn 70). Buy upgrades and improvements for your clients to be happy and leave tips. Good luck!
Click on a customer and then on the table where he will sit; then click him to know his order, click the order when it's ready on the bar, then click again the customer to deliver the order, and so on with the rest.