There are many kinds of fabric that can be used to make clothes such as cotton, denim, silk, satin, linen, wool, and flannel. Each fabric offers a different look and feel to it. For example, denim is a heavy fabric that does not stretch, linen conducts heat, and silk is shimmery with a slippery feel.
If you have clothes that you no longer use, simply take apart at the seams and reuse the fabric for other clothes, or quilts, or whatever you want. If you want to make the clothes into other clothes. The most common 'remake' is to cut off the bottom of an old pair of pants and transform it into a pair of summer shorts. Another common remake is to take a skirt, take apart the seams…
Textiles is a course that you can take in school, or even outside of school. It is a course for fashion design. You sew and make clothes and projects of fabric, and they teach you how to use different sorts of materials for clothing. You also learn different sorts of fabric, and how to make different clothing items.
You can buy patterns in fabric stores (or fabric departments of department stores), buy fabric and cut it to fit the patterns, then sew the cut fabric together. If you don't know how to operate a sewing machine... ask someone to show you how, and PRACTICE before you spend a lot of money on dress materials. (Hand-sewing clothes can take forever.)