Hi Mary, sorry it is confusing for you. Here is a picture of a bolt of fabric telling how to tell the straight of fabric. In the little drawings on the pattern cutting instructions I show the selvage edge and the fold. This picture of the bolt shows where those things are.
If your fabric is cotton, almost all cotton has the selvage on the straight grain of the fabric. Cotton that is 65% polyester may not– but I have yet to see any that didn’t have the grain running in the same direction as the selvage edge.
Dupioni Silk has the grain running across the width, instead of the length of the fabric, but you can plainly see it and tell by looking. Fabrics like silk and satin and taffeta may also have the grain across instead of the length of the fabric, but I doubt you are using those.
If you are using a piece of cotton that has no selvage edges, another way to find the straight grain is to tear it– make a cut like you were going to cut off an inch and a half of the fabric– you have to cut it in a couple inches to get a good grip– and try to tear a strip off the fabric. It will tear easily ACROSS the grain ( as though you were tearing from selvage to selvage) but fabric will NOT tear easily WITH the grain.It will pull threads and look ragged. This does waste fabric and hopefully you won’t have to do it– if you have even one selvage edge left it is easy to find the grain.
If you have something like an old sheet, try tearing it in two directions– and it will tear smoothly ACROSS the grain, but NOT on the grain of the fabric. You can then use the old sheet to make a prototype of the dress. You don’t need to finish anything when you make a prototype! Just cut out the bodice pieces, sleeves and skirt. Sew up the should seams, don’t finish the neck or anything, set the sleeve in for practice ( don’t finish the bottoms either) then cut the skirt and gather it to fit– no need to finish the back or hem it to then see how the prototype works. This will take the fear out of using the pattern! Sometimes when I am making a new pattern, I will make 4-5 prototypes before it is perfected! Old sheets are GREAT for this!
If you need more help, Mary, do feel free to call me!