A few weeks before your villager's birthday, Tom Nook will post a notice on the bulletin board announcing which villager's birthday is approaching. You will know that there is a new memo because a bird will hang at the top of the memo board.
If you miss the memo, your other villagers will also mention your villager's birthday when they talk to them. If you want to find out if any villagers are celebrating their birthdays this month, you can find many informal villager birthday guides online, or you can buy the official Animal Crossing villager birthday guides from MyNintendo. The villagers in the animal forest are collectively referred to as ACNH Items here, you can get them on the ACBellsBuy site include ACNH Nook Miles Tickets.
If you want to increase your friendship with the villagers, you can choose to visit them on their birthdays. You just need to show up at their house, where they will hold their birthday party. Best to bring them gifts. If you attend their party, they will send you a letter and a gift the next day, thanking you for attending their party.
Your villagers will also celebrate your birthday with you
When you log in for your birthday, your villagers will host a birthday party for you in the game. After logging in, one of your novice villagers or one of your best friends in the game will be waiting for you outside the house. They will invite you to their house for a surprise, and the other two villagers will be here waiting for you to celebrate.
There will be a piece of cake in the center of the room, you can press "A" to blow it out. Then replace the cake with a faience pot, you can click on the pot to reveal 10 birthday cakes. These can be provided to other villagers who did not attend your party.
You can buy villagers with the same birthday from the ACBellsBuy site so that you can celebrate birthdays for two villagers at the same time on the birthday. ACNH Bells is the best-selling product of ACBellsBuy. Busy players will also Nook Miles Tickets Buy from ACBellsBuy, which also means that ACBellsBuy is a trusted website!