From Nookipedia, the Animal Crossing wiki
The acorn types are:
To improve the chance of collecting all 230 acorns needed, the player can plant as many oak trees as possible before and during the Acorn Festival.
After collecting the acorns, the player can hand them in to Cornimer in exchange for furniture from the Mushroom Series. Cornimer will be standing outside the Town Hall and will keep track of all the acorns handed to him, providing a piece of furniture every time a certain acorn count is reached in accordance to the following guide:
However, handing Cornimer any rotten acorns will result in Cornimer taking the whole batch without anything being added to the player's score.
Alternatively, the acorns can be traded in to Tom Nook for 100 Bells each. Left over acorns will remain on the ground a few days after the festival. Sometimes, residents in the town may ask the player for an acorn, and will give a pitfall seed or stationery in return.