Solids for newbies

Hi folks. I’m trying to create a solid object for 3D printing. Have made the drawing (but not in a very clever way I guess). It’s obviously not a solid but is there a simple way to turn it into now or do I start form scratch and do it ‘properly’ somehow? To share the drawing here do I just send a hyperlink?
many thanks

If you are using the Web version, use the Download option found top left to save the model to your computer, then use the upload icon at the top middle of the reply window to attach it.