I will second the recomendation on ordering a copy of Barb's book "The Art of Kiltmaking". It will answer all your questions about what the parts of your kilt are, what they are called, and why they are there.

One comment, The Hair canvas that is inside the kilt is not just a band stuck in there to thicken the kilt it is actually the interfacing that keeps the entire kilt hanging correctly and not warping out of shape.

If you imagine this...take a piece of hair canvas and fasten straps and buckles to it. Then strap the canvas around yourself nice and snug and into the small of your back. This interfacing is what you are actually wearing. The Tartan fabric can then float over the canvas without being distorted or having stress placed on the stitching.

If you have a kilt that the pleats are cut away to thin the kilt at the small of the back but the interfacing is missing then to put it back in is not a small job. Not impossible but you need to remove the liner completly. Remove the straps and buckles. Then place the hair canvas into the kilt and sew he straps and buckles through the Tartan and onto the interfacing. Then you replace the liner to cover everything up and look nice and neat.

Also....The Steeking is a line of stitches done on the inside to hold and support the inside of the pleats where they have been cut. This holds the pleats in position and parallel so they won't curl. (Way2fractious is correct. Steeking = Gaelic for "To Stitch".)

good luck. and remember to post pics of your work when your done.