Hey Schmetterling!
Its awesome that you are interested in sewing!! First thing I would suggest, since you are capable of teaching youself, is getting a hold of the
Readers Digest Complete guide to sewing. You don't need to get the most current edition. The only difference I've found so far in the different versions, is the projects are more modern.
To get you started though, your first step will be finding a pattern that will work with the type of fabric you have. On the back of a pattern envelope, it will list near the top all the recommended fabrics. You would be looking for a dress that recommends using a cotton fabric. The pattern will also tell you how much fabric you will need to complete the project, and what other supplies (hook and eye, zippers, elastics, facings, interfacings, etc. ) you will need to buy.
The first thing you will need to do with your fabric is wash it.
The next thing is to straighten it. In order to straighten it, you will want to put both salvage edges together (the salvage edge is on each side of the fabric width, on most quilter fabrics it is white). That means folding the width of the fabric in half. Then you will need to hold the fabric up and see if, at the bottom, the edges still match. Usually they wont, showing that the threads in the fabric are crooked.
I will need to get back to you about how to straighten your fabric. i don't know how to describe it with words!
Let me know if I'm making sense so far