Creating New Images in Preview
No it isn't possible to create new images with Preview, as it is just meant for doing basic edits on images.(see @SteveChambers' comment)

If you really want to use Preview and not another app, just find a white image of the size you want and open it in Preview to edit and draw on it.

Otherwise, you can use 3rd party software:


GIMP, a free and open-source image editor with many capabilities, including creating and drawing images(fun fact: the very first Google logo was created in this program)
Keynote, made by Apple as a presentation app, but can also be used for simple drawings
Pixelmator (paid), a user-friendly image editor with many drawing/painting capabilities
Acorn (paid), a user-friendly image editor with many drawing/painting capabilities