When you first start out in Clover Town, there are not a lot of people around. The local villagers are meagerly getting by but the town is slowly decaying. Not even Mayor Jarvis knows what to do.
As you develop your farm and shop, new visitors will come to visit the town. When you go to bed at the end of your play session, you will be told if a new "reservation" has been made. A reservation will include the date the person is going to appear in your town, and a silhouette of what he or she looks like.
The villagers who live in Clover Town are new characters, but the characters that visit (by reservation or random) are from past (and future) Harvest Moon games. Some may be customers to your shop, and appear in the Customer List on your house table, while others are just there to talk to.
Every day you will find a different set of villagers standing around your town. Not every person is in Clover Town on every day. Non-customers like Ellen may only appear during festivals.
Each shop has two shopkeepers, and they will rotate in and out of the shop. On some days you may find Cynthia outside of the tool shop, while on other days you'll find her brother Daniel. The same goes for Mint and Nick, Takakura and Danica, and Rebecca and Cecil.
These characters will only appear in your game if you buy the additional add-on packages: