Yank lines 81-91
:81,91y<enter>
If your fingers don’t like to find the : and , keys, this would work as well (go to line 81, yank 11 lines)
81gg11yy
My only use of g is 5gg. To go to the 5th line. 22gg: 22nd line. As jimbo said, it’s really only a modifier for some other commands.
For completeness, (http://vim.wikia.com/wiki/Power_of_g) explains a lot of how g works in command mode.