Check this FAQ entry. It contains a pair of video links in addition to the text.

Probably best to use one of the roof tile fills from one of the city styles?

Normally, you shouldn't need to change anything, as the tools and sheets should be set up to make everything just work unless you are trying some more advanced techniques.

Looking at your screenshot, I notice the Sheet setting for the tool is blank. The default setting for that particular tool should be LAKES*.

With that setting blank, it means that CC3+ will NOT attempt to put it on the correct sheet automatically, meaning you'll have to take care of things manually. Basically, that means you need to set the sheet to LAKES manually before starting drawing. I see it is set to LAKES currently in your screenshot, so assuming that your landmass is indeed on the LAND sheet, it should work right now, but if you change the currently set sheet, it will go to that one instead.

If it doesn't, confirm that your landmass is indeed on the LAND sheet, as rearranging sheets won't do a thing if entities aren't on the appropriate sheets.

Basically, use Info -> List on your landmass to check it is on the LAND sheet, on the lake to check that it is on the LAKES sheet, and that the sheet ordering is with LAND appearing higher up in the list than LAKES.

And to add what Loopysue said, make sure that your rivers and lakes really are on those sheets. They won't automatically go there even if you have sheets by those names, where they go is determined by the setting in the drawing tool.

You can always check witch sheet an entity is on by using the the List command from the Info menu, or simply hiding all other sheets than the one you wish to inspect.

Try right clicking the zoom button and do a zoom to all text. Assuming there is any text in the map at all, just click one of the entries to zoom to it. Then try Sue's procedure again.