How to properly position first person 3D Item?

Hey guys,

I managed to add animated guns with arms in MCreator, but the thing is, how do I position it so it looks normal? And how do I configure, so that the "arm" has the same texture as player?
Not sure if I missed it, but in Blockbench, I couldn't find anything to display the position.
Same question goes to how to animate for thirdperson.