When mitring by hand, you will need a few tools to get started. You will need a saw (a coping saw or small handsaw is best), a mitre box, a hammer and chisel, and some sandpaper. The first step is to set up your mitre box. Place the mitre box on a stable surface and clamp it down so it doesn't move around while you're working. Then, use your saw to cut along the lines in the mitre box. It's important to make sure that your cuts are straight and accurate - if they're not, your finished product won't look as good.
Once you've made your cuts, use the hammer and chisel to clean up any rough edges. Then, sand everything down until it's smooth. Now you're ready to assemble your project!