Do you mean you want to use Aulani's pool? Unless you are a guest of Aulani you are not allowed to use their pool. They are strict on this and everyone must wear a bracelet.
You are fine to walk through the resort, dine at any of their restaurants, buy at their shops and use the lagoon as the lagoon is a public lagoon.
The only "charge" would be the $35 parking fee but if you buy stuff there (souvenirs, restaurants...) over that amount you can get it validated so parking is effectively free.
Just to perhaps state the obvious, Aulani is not an amusement park a la Disneyland. It's a resort hotel with some kid friendly pools and a few Disney characters.
And if you see Disney characters taking photos with people you must be a guest and they check either foryour bracelet or a room key.
As everyone has said, you may visit Aulani and tour the shops, enjoy the restaurants but not use any of the facilities. Maybe you could add a day on to your vacation to stay to enjoy the resort.
Ok thanks everyone