Wash your glass with mild soap and water or rubbing alcohol; let dry.
Cut circles of various sizes from the tissue paper using either a die cutter or a template. Cut out enough to cover the jar(s).
Place a thin layer of Mod Podge down on the jar in a small area. Place one circle down on the top and smooth lightly with your brush. Don't overbrush or you'll tear the circle.
Repeat with additional circles, overlapping as you go. Layering circles of various colors and sizes makes a color effect. Wipe away excess Mod Podge when necessary.
Once the entire jar is finished, let dry. Then apply two coats of Mod Podge over the top of the jar, letting dry between each.
Video
Notes
Trim the edges of the jar with a craft knife before using, if any paper dries over the edges.