StoryBoarder is free open source software for creating story boards.
Strory Boarder can be downloaded from: https://github.com/wonderunit/storyboarder/releases
Find the latest stable version and then download and run the installer for your system. (The installers are in the assets section: exe for windows, dmg for mac, appimage for linux)
When you start story boarder you will see this screen. You can click Create New Storyboard
If you have a script, You can load it in and then storyboarder will display it side by side with your storyboard and allow you to link boards to specific parts of your script.
Other wise you can create a blank storyboard.
When you create a new project, story Boarder will ask you about aspect ratio. Choose appropriately.
Once you choose one of these options, Storyboarder will ask you to create a new save file for your StoryBoarder Project.
Here you can see the interface. If you chose to use a script it will appear on the left side. In the Center is your canvas for drawing your Panel. Along the top are some different tools for painting and drawing. along the bottom you have the sequence of your boards. On the right hand side is where you can configure the properties of the current panel as well as opening the shot generator.
The shot generator is a really fun, and useful tool for laying out scenes, experimenting with shot sizes, framing, and camera angles, and creating boards quickly without drawing. You can open it, by clicking the panel under the words Shot Generator on the right hand side.
In the shot generator, you layout your scenes in 3D. By moving your subjects and camera around, you can create unique and interesting shots for your film.
Go ahead and explore Storyboarder a bit.