Re-Logic said that their goal with Journey Mode is to "provide a more accessible experience by providing the player unprecedented control over the gameplay experience". They make it sound like it's a Creative Mode like seen in many others but it's a lot more than that, it's an entirely different way to play. So different in fact, Journey Mode has its own character saves and you can't mix characters between modes.
In this new mode you will start off with these items:
- Iron Shortsword
- Iron Axe
- Iron Pickaxe
- Iron Hammer
- Finch Staff (a bird that is happy to sit on your head when it isn't attacking your foes)
- 100 Torches
- 100 Rope
- Magic Mirror
- Starter Wings (very limited flight, removes fall damage)
From there, you will then need to do research. Once you research an item, you will then be able to duplicate it as much as you like. However, you will first need to dump a certain amount of whatever it is you're trying to research to unlock the duplication:
So it's not a true creative mode but somewhat close. This system works across multiplayer too.
On top of that you will gain access to control the weather, manipulate time, spawn rates for enemies, a Godmode (good for kids), massively increased placement range and more. Terraria 1.4 Journey's End will also have a Master Mode, which as the name suggests will be quite difficult. Journey Mode appears to be able to let you change the difficulty at any time too. See more here.
Re-Logic also allowed ChippyGaming to take an early look, which you can see below: