Experience and Levelling Up
Experience is gained from doing a variety of things. Mainly, it comes from producing food. Each batch of food gives you a certain amount of XP, which is then used to level up. The more you level up, the more difficult (and pricey) the cakes you can make.
You can also buy new items and expand your bakery to a greater degree.
Levelling up allows you to have more appliances in your bakery, giving access to more recipes too!
Experience is indicated by the yellow bar in the middle at the top. You will see a star, showing exactly what level it is that you are currently on. You should always be aiming to increase your present level. The bar itself will turn yellower as you come closer to the next level. You will then gain access to all new recipes and items with your newfound expertise.