Root on low E
355xxx
G5 is the G power chord. Its notes are G and D. No third means no major or minor quality. Mute unused strings carefully.
355xxx
x-10-12-12-x-x
Numbers show frets from the low E string to the high e string; x means don't play that string.
Every G and D on the first 12 frets. The filled dots are the root, G. Build your own shape from any nearby group.
Other G chords
Other power chords