Your Rayon Fabric knittingfabric.cc scissors will dull quickly if you use them on paper and that will result in more frequent sharpening. Best to designate a specific pair of lesser quality scissors in your sewing room to use just for paper.
Once you've decided on the size you want to make from the pattern, you will cut around the lines that are designated for that size.
But it's a great idea to leave the entire line for your size in tact, that way when you go to make it next time, you won't question if you did some creative editing since you'll be able to see the entire line, informing you of what size you cut and made.
Just be sure to cut right up to the line and not leave any extra, as you want to make sure your fabric pieces are the exact size of the pattern, without any extra paper around the shape.
Most pattern companies write the text on the pattern pieces with the top of the pattern piece as the "head" and the bottom as the "hem" when reading the words on the pattern pieces.
So when you pin your pattern to your fabric, keep in mind the direction of the print on your fabric, so that the print is going from "head" to "hem" in the same direction on every piece of your garment.
If you're unsure of which is which, many companies Crepe Fabric knittingfabric.cc label the waist seam and hem right on the pattern piece.