Brass marching bands will often use open-ended instrument covers to display the logo of their group. A whole group all sporting the band logo on their instruments gives a professional uniform appearance. A slide cover should be easy to fit and remove quickly without anything needing to be permanently fitted to the instrument. They also shouldn't interfere with the sound or playability of your trombone. The logo can be embroidered, a printed transfer or a sew-on patch.
Lay the sheet of nylon next to the slide. Trim it for length; it should reach from the second horizontal strut at the joint to the point at the tip of the slide where it starts to curve around.
Lay the slide on top of the cover, directly in the center of the fabric, leaving a flap at either side. Fold the flaps over to check the width of the fabric. There should be a roughly 1-inch gap between the edges; they shouldn't overlap. Trim off any excess from the edges to ensure that the gap is the right size.
Remove the fabric from the slide and load a pair of eyelet pieces into the punch. Punch an eyelet into the fabric along the edges, spaced at roughly 4-inch intervals. Repeat down the opposite side.
Lay the slide back onto the fabric and thread the shoelace through the par of eyelets nearest the rounded end. Lace up the eyelets as if lacing a shoe. Gently pull the laces tight after threading through each pair of eyelets. When you get to the top, tie the excess length around the horizontal strut, to prevent the cover from slipping off the slide.