Look at a guitar chart for the fingerings for G, C and D. Play the G chord for the words "Silent night, holy night." Next, play the D chord for "All is calm," then back to G for "all is bright."
On "Round yon virgin" play C, then return to G for "mother and child." Repeat the C to G pattern for "Holy infant, so tender and mild."
Play D for the beginning of "Sleep in heavenly peace," switching to G on peace. For the repeat of that phrase start on G, switch to D on "heavenly" and return to G on "peace."