Trussing a bird for roasting means to tie it in a neat bundle, which helps with the roasting, presentation, and carving. There are many methods and devices used for trussing, but for me, the simplest is the best.
All you need is a length of good, strong, undyed cotton kitchen string.
Cut off the first two joints of the wing.
Push the tail of the bird into the body cavity.
Wrap a length of string around the legs and tail sections and cross over as shown. Bring the string between the drumsticks and breast to the front of the bird.
Turn the bird breast side down and tie the string securely across the back, in front of the wings.