The tweet literally tells you exactly what the green and yellow bars are for. Green are turns and yellow is health.
How am i supposed to know that the green bar was the turns? (It was looking green so i was assuming that the system would work like that), it would have bee nice if there were letters saying "HP Bar, Turn Bar", i was also confused about the health of the enemies being yellow instead of green so, well, that left me confused, outside of that, there is the other problem about the commands, let's say that is your turn, the only thing i can see plausible (or basic) from the looks of it are the commands "Fight", "Special Attack, "Items", "Defense", "Run or Escape". Those are the most basic choices in most rpg's, and pretty much the common standard, since this is a turn side game, those are the most probably choices for the command settings, since this is a 2d rpg game with a little mix of action and platforming (apparently).
I'm pretty sure that it's setup so that they can draw a weapon over her hands, and also not have the weapon be part of her. it's pretty clear and a post a few posts behind you kind of makes it clear!
if you mean overworld, well.. um.. ummm
As i said, this is a prototype image so, anything about the stances will be fixed in the right time, and speaking of the overworld, by what i have seen from the early alpha beta gamma video (With the cat in the background) the overworld will probably work as the Vanillaware games, such as Odin Sphere or Muramasa: The Demon Blades, for those who don't know, every Vanillaware game is in 2D (Since George Kamitani stated that this is the best approach to work in his videogames) and therefore they created several action RPG's (Actually only about 3 or 4, not counting GrimGrimoire since it's a tactical game, but anyways) the overworld works like this
Let's say, Ajna is in the frozen mountains, and she need to go to the ruins, then, this over-world setting may work for different reasons, the main reason being the change of an environment, if we assume that Indivisible will be set in a place jungle - ruins style, then, this will not be necessary, but, in order to expand the game, you would have to create several different locations, and to create those several different locations you will need something like a Map Over-world, because you will have to expand the new world instead of the journey between Ajna is placed and the next new world, country, or setting. You can also see an over-world part of where she lives, so you may also understand the principal setting, a Map will be mandatory, and therefore, this setting is realistically and most plausible way to achieve for the game.