The Wiremold website is fairly helpful but lacks some detail. You need to buy a small installation kit for the molding. It has both exposed clips (small brackets) and concealed clips that screw to the wall and are used for attaching the molding to the wall.
Start at the place where the wiring exits the wall or otherwise will be fed into your Wiremold run. Install a Wiremold electrical box at that location and then measure, cut, and install the Wiremold conduit, elbows, and conduit where you need it. You should plan the system in advance but cut as you go.
Keep everything level and make sure that you follow all codes. I'm not an electrician.