A Pacapaca is the games version of an alpaca. It is automatically put into your storage, and may be taken out by talking to 'Animal Lady' and sending it to the barn, after you vist 'Hill Fort' for the first time.
It can be talked to, to check how they're doing. It can be fed produce by putting crops you have harvested in the 'Feed Box'
After some time you'll be rewarded for your efforts by wool, which can be sold.