If a brand new stencil is needed, then there is a simple process in order for one to be created.
First, as a web author, create a new model as normal and save it.
Once this is done, download the model.
Now go on to browse, click 'Systems', and then 'Stencils'. Add a new folder and upload the file that you have just downloaded.
Once the file has been uploaded, the file name will be displayed in the Stencils folder.
Now, when you go to create a new model under Author, you will see your new stencil as an option.