The Restaurant is the place where you go to buy food. The Restaurant is open from 6am to 6pm, Monday through Saturday. Rose is in charge of the shop.
Having a supply of food is important to keeping you healthy. You eat automatically when you wake up in the morning (6AM), once in the afternoon (12PM), and once at night (6PM). If you choose to go to bed before 6PM you don't eat.
Rosie will sell you your supply of provisions. She sells them in packs of 10 or as single servings. The single servings you eat immediately at the shop and the packs you reserve for later use. If you become incredibly weak during the day due to hard work and you want to continue working, you can run to Rose's and buy single serving food items. Single serving foods replenish your energy so you can continue working. It works much faster then sitting in the Hot Springs, plus you can also replenish all of your energy. You can't do that with the Hot Springs.
Later on in the game Chocola will take over the Restaurant. More information on that is located in the Unscheduled Events Section.
To know how much food you have in reserve, go into your house and look at your stove. The stove is located in the lower right corner of your house. Pressing the A BUTTON next to the stove will let you know how much food you have left over.