Pick up the 2-by-4 piece of lumber that is 48 inches long. Put it on top of two 2-by-4 pieces of lumber, each 84 inches long, to create a simple wood arch. Use wood glue to secure each corner with all pieces meeting flush, and let dry.
Use a 9/64-inch drill bit to create two centered pilot holes on each of the 84-inch side poles by drilling down through the 48-inch wood into the 84-inch pieces. This will help secure the 48-inch piece of wood as the top of the arch. Use a No. 3 Phillips head point size drill attachment and four No. 13 tapered flat-head wood screws to attach the two corners together. Sink each screw slightly below the wood surface using the pilot holes to guide the screws.
Lay the assembled arch on its side, and center it on a 4-by-8 foot piece of plywood for a stable base. From underneath the plywood, drill two 3/4-inch holes through the plywood and into each of the 84-inch pieces of lumber with a 9/64-inch drill bit. Then use the No. 3 Phillips head point size drill attachment and four No. 13 tapered flat-head wood screws to attach the 84-inch pieces of lumber to the plywood base.
Stand the arch upright, and wind 50 feet of pliable vine around the arch. Add 20 to 40 floral pieces to the grapevine in random places, secured with floral wire.
Cover the base of the arch with pine mulch to complete the archway.