No. Your fingers are not the cause!
There are a few reasons why you may not be seeing any marks on the canvas when trying to paint or draw a brushstroke.
If the canvas is blank and the current brush mode is the Eraser. Open the Brush menu and make sure the color is different from the canvas.
If the opacity of the current brush is 0%, then brush strokes will have no effect on the canvas.
If the current color is exactly the same as the color on the canvas, then brush strokes will have no effect in this case either. Open the Color menu and make sure the currently selected color is different from the color on the canvas.