you will get there by doing main quest. need a special ship that you get in game
To piggyback on that, you must follow the main quest storyline all through Cool Ranch. Eventually you'll make it to Tumbleweed skyway. After that, you'll go to Haunted skyway. There, after a small amount of questing before, you'll be sent to a dungeon called Miranda. After you defeat Captain Blood, you'll be sent to Motherlode Mine where you will have to defeat Deacon, receive the ship BillyBobby781 was talking about about and be sent off to talk to a few people. Then, after talking to Captain Avery, you will be granted access to Mooshu.