In the Content tab click on "+New Unit" toward the top left of the page.

Title your module, then add a description due date and availability/release dates if you like. Click the blue "Save and Close" button. Your new module will appear at the bottom of the module list. To add a submodule, click into the module you want to add it to. Then click on "Create New" at the top right of the page.

Click on "New Lesson" 

Then add a description, due date, and availability/release dates if you like. Click the blue "Save and Close" button. Your new submodule will appear at the bottom of the module list.