Do not cut a curve! These are instructions for a simple tube skirt with an elastic waist.
1. Sew the ends of the fabric together, right sides touching, so you have a tube of fabric.
2. Now you can either zig-zag stitch over the raw edges at top and bottom (so they don't fray) or you can fold them over about a 1/4 inch and iron (so when you sew the hem and create the elastic casing the raw edges will be encased)
3. On the edge that will be the waist fold the fabric over about a 1/4 inch wider than the elastic you have. Iron it so it creases and use pins to keep it still.
So if your elastic is 3/4 of an inch wide fold over an inch. If it's an inch wide fold over an inch and a 1/4. Being exact isn't really important as long as you don't short it. When in doubt, fold over a bit too much rather than too little.
4. Starting an inch or 2 past the seam in your tube, sew down the edge of the fabric you folded over. Stop an inch or 2 before you get to the seam. You're making a casing for the elastic to go in. You want to leave an opening 2 or 3 inches wide to insert the elastic.
5. cut the elastic to the same measurement as your dd's waist. Attach a safety pin to one end and feed it through the casing you made. (Don't forget to hold on to the other end so it dosen't get lost in the casing) When you have the elastic through the casing and both ends showing through the gap in the casing make sure it's not twisted anywhere in the casing then overlap the ends and sew together with a zig-zig stitch.
6. Sew the gap in the casing closed.
7. Hem the skirt and you're finished!