To figure out how much fabric you need, lay a jar onto the fabric and roll it up in it. Leave about an inch of extra fabric at both the top and bottom of the jar. Trim to fit around the jar, leaving yourself an inch or so extra. You can always trim the excess off if you need to.
Paint the jar with Mod Podge. Lay the jar onto the fabric and use your fingers to press the fabric to the glass. Cut slits in the fabric overage at the top of the jar to make it easier to fold inside. Add some Mod Podge to the inside of the mouth of the jar and press the fabric inside. Repeat this process for the bottom of the jar. Set these aside to dry.
Cut strips of felt and hot glue them around the rim of the jar. Hot glue buttons onto the felt to embellish.