As you can see in the video, I made a circle, then coloured it in manually - and then, it went over the outline.
How do you avoid this? I would like to colour an object without having to go through the hassle of carefully erasing it.
It's probably best to create a vector layer. Then make a circle. Then select the circle with the Select Shapes tool.
Then you can change the stroke and fill in the Tool Options. Because the object is a vector, you can do this as many times as you like.
Although changing the fill here looks like I'm using the Fill Bucket tool, it's not the same thing. The fill is actually part of the vector shape itself.
Note: Vector shapes are not limited to just circles or geometric shapes. You can create your own vector shapes with the Bézier Curve tool, and similarly apply strokes and fills to it.