Once found, a Secret Note can be read by selecting it in the top row of inventory and right-clicking (as if consuming food). This will add the note to the player's collection, and enable the Secret Notes collection tab on the player menu.
Some notes will list "Loved" gifts for certain characters, while others will have images depicting puzzle solutions. Reading notes that list gift preferences will add the gifts to the villager's Gift Log on the Social tab of the player menu.
Secret Notes can be gifted, but they are all [[Friendship#Universal Hates|universally hated]].