how do i make add MouseButton1Click inside StarterCharacter

[spiral eagle]

local scripts work if u put them inside the character

or any descendant of it

[white oriole]

That might be your best solution 4 now

but I wouldn't use UIS

compatability-wise

it will be difficult to work with 4 mobile devices

so use ContextActionService

CAS

https://create.roblox.com/docs/reference/engine/classes/ContextActionService

always size a UI element (1,1,1,1) before you try to manipulate it

that way it'll get its scaling correct

you can also use a plugin called "AutoScaleLite"