Quote:....I've been using photoshop for years and wanted to get off the Adobe train...
The hardest part is accepting that Gimp (or any other graphics program) is not PS and never will be PS.
The documentation is quite extensive. https://docs.gimp.org/2.10/en/gimp-file-new.html
The File -> New for a new canvas has an advanced section where there is a drop down menu with various options for a fill colour
The default is the current background colour so you could set that before File -> New.
I usually start with a white canvas anyway. Want something else? Use the bucket fill tool where there are settings for FG/BG/pattern and fill the canvas. Another way is click-drag-drop from either the FG or BG swatch. Dragging from the patterns dock works as well. Quick and easy way to fill the canvas / layers / selections, give it a try.