Position the hay bales according to your party needs. If you are trying to encourage a casual atmosphere the bales can go in a circle. A more formal atmosphere will be enhanced by placing the bales in lines to form rows of seating.
Spread the tarp over the hay bale so the edges of the tarp drape the ground.
Lift the hay bale up about four inches so the front edge is off of the ground. Tuck the part of the tarp that is draped on the ground under the edge of the bale. Repeat this on the back edge of the bale. Tucking the tarp under will prevent tripping accidents.
Put the end of the rope through the lower front grommet hole on the tarp. The grommet is a metal piece with a hole in the center and it will be right along the edge of the tarp.
Weave the rope across the end of the bale to the lowest grommet on the back edge of the bale. Weave it up the end of the bale and through the grommet nearest the top front edge. If there are any places where the tarp sticks up look for an empty grommet to fasten the rope or run a second line of rope through a grommet you are already using. Then pull the rope snug and tie it to hold the tarp on the bales.