To create a board, either choose "Boards" in the left sidebar and click "Create board", or go to Workspace --> Overview --> "Create board".
When you create a board, you have to choose which template you want to use. You can start with a blank board, a simple to-do list or a more advanced template, like Business Model Canvas. If you want more information about a template before choosing, you can click "See more details" under the template.
When you have decided on a template, give the board a name, select a visibility setting and choose which team you want to create the board in.
Now you are ready to start adding cards!