Click Share at the bottom of the screen to do this. Note that yuo can not remove permission (either view or edit) once you give them. You should backup your family tree everytime you make changes if you give anyone else editing rights. You could also export the GEDCOM file and send that to them if you think they can figure out what to do with a GEDCOM file. You could also send them a PDF. You could also export your site as HTML and put it on a webpage somewhere.
