The thing about LocalStorage is its asynchronous. You can't just do what you'd normally do, read and write data on demand.
Local Storage is a bit like interrogating a rather slow person on the other end of the phone e.g. to get (say) a high score
1) Action "Check Item" (Ask it if the high score exists) by key (e.g. "myGameHighScore")
2a) On event "On Item Missing" (No), set the default high score
2b) On event "On Item Exists" (Yes), then action "Get Item" (ask what the value of "myGameHighScore" is)
3) If you asked "Get Item" On event "On Item Get" (Here it is) you can retrieve the actual value (from ItemValue member)