Measure the width and length of the furniture that you want to upholster. Choose fabric of whatever type and color you want. Use premeasured fabric, which you can easily find at a fabric store. Start with your cushions. Make sure you have enough material so you can cover both sides. Buy thick foam from a craft store or fabric store if the furniture doesn't already have it. Sew two sides of the fabric together so that there is one open side -- you will have wrapped one piece around. Reinforce it as you move along. Slip the cushion inside and sew the edge closed.
Remove old screws with a screwdriver or remove nails with the back of a hammer. Prepare a 1-inch-thick slice of precut foam. The foam will be thicker if you are upholstering a sofa or cozy chair. Pop the old seat out if you can. Unscrew or take out the nails of the seat if you can access them. This could make Step 3 easier, but keep the seat in if it's too difficult.
Apply white glue designed for foam to the seat in lines. Move the glue in relatively thin streaks down and up. Do the same on the foam surface. Place the foam on the seat exactly where you want to keep it. Press it down. Allow it to dry for two hours.
Cover the foam with premeasured fabric by stapling it to the bottom of the arms and to the bottom of the front and back of the seat. Ensure the fabric is tight before you staple it. Do your best to nestle the staples in where they are hidden. Cut off any excess fabric. Put the cushions on the fabric.
Place the premeasured upholstery at the back of the furniture. Pull it tight and staple it to the frame. Complete the same process on the arms. Trim excess material.