Here you won't really need any resources.
Although, you do need to use several things. They are a sheet of paper and a pencil. You don't have to be a professional artist. No need to be an artist at all, to be honest. Storyboards are timesaving means: you already know what illustration you would need, what would the layout look like and how many slides there would be even before you have opened PowerPoint. You may want to change something at the stage of design, and it is absolutely fine if the storyboard and the final result do not match. What matters is that you have a starting point, a prototype - your storyboard. Here are several examples: