Okay so, i know its possible to make it from (Vector3 & Vector3) to UDim2, but i dont know how to make it turned around. Like for example, i want to have Vector2 of a Button in the players screen.
Okay so:
What would you need to do to convert that UDim2 to a Vector2?
Okay, so if I am understanding you correctly, you simply want to convert the datatype Vector2 to a UDim2? I wasn't sure what you meant, so I prepared three replies.
Casting GUI object to 3D space I thought you might have meant this. I searched maybe twenty minuets, but I wasn't able to see anything. Unfortunately, I don't see any easy way to cast a GUI object on a player's screen to a position in the 3D environment.
Simply Converting Types I'm not sure why you would need to do this, but I thought there was a possibly that you might need to cast the one type to the other, maybe because you need a method only available in UDim2? Anyways, that's simple. You would just do something like this, with A and B being Vector2s you pass as arguments, and C being the UDim2 output.
local C = UDim2.new(A.X, A.Y, B.X, B.Y)
I do, however, assume this isn't what you need, since that doesn't seem to pose any usages, and I don't see any real reason for it.
Having the player click a button on a Billboard GUI This one is actually quite easy. In fact, in really only requires a few extra steps. Instead of putting it on the block itself, have a code put it in each new player's PlayerGui. Just make sure to set the adorne value to what block is should be shown on. Now, you can use the GUI similar to a ScreenGUI. Like magic!
In case you're a little confused, I created an example world, with a very simple Billboard GUI, with a single button on it. When you join, you're able to click that button. I uploaded it to my GitLabs server here
I hope I was able to solve your question, if so, please mark my answer as accepted, if not, please respond to me, so I can see if I can help you out.