Use two sheets of plywood, on a flat surface. Draw your picture/pattern on the top sheet. The bottowm sheet might get scarred, but bettter it than your front porch or table. Set the depth of your router to the depth of 1 sheet of plywood. Using a cutoff bit plunge it into the sheet of plywood on the outside of your pattern and then follow the pattern you have drawn. Pull the router don't push. Use a steady slow motion.
Always use saftey. Don't let the router get away from you.
Plunge the bit on the waste side of the pattern. inside or out depending on which side you wish to keep.
IMHO, for someone unfamiliar with power tools this task is better approached with a jig saw. Freehand pattern routing on that scale doesn't seem like a good choice for a first woodworking project.