I know that this is an old lesson, but for those who are confused as to why filling color on another layer that has an outline ended up filling the entire pages with color, you can change the setting of the fill tool to look at all the layers that have been created. I experienced this and was confused if there is a setting I misconfigured. This can be done in the tool option (usually bottom right) and scrolling down on the "reference" section. From there, pick the one where there are 3 squares stacked on top of each other. Now, you should be able to fill a layer with a color from another layer, like the video.