Parse.com: Cache Policy vs LocalDatastore

Question

I am very new to Parse with IOS and I am very confused about Cache and LocalDatastore. What is the different between kPFCachePolicyCacheOnly and fromLocalDatastore. Should I use localDataStore intead of Cacheonly to support offline usability. Basically I want to make sure that when it's offline, the user can still get the information that he has achieved when he is online.

Thanks