Setting a game size

Hi,

I am trying to build my first unity game, but I am struggling to understand how to set up the resolution. I have produced an initial graphic for the game, in 1920x1080, but the resolution of the canvas in unity is something like 854 x 1560. Obviously, my design doesn't fit, and so there are bars around the image when I set 1920x1080 in the game preview tab.

How do I configure the project to work with 1920x1080 full screen, whilst also making work across other resolutions?

Thanks DcoltGaming