Use a piece of chalk to draw an outline of the design to cut on the wood. If it has to be precise, use a measuring tool like a ruler or protractor to ensure your outline is accurate based on the required design specifications.
Put on your gloves and goggles for safety.
Secure some scrap or extra wood with sandbags or other heavy objects so it does not move when carving with the chainsaw, then turn on the chainsaw. Practice a few cuts on the scrap wood, especially if you haven't used a chainsaw in a while. This helps you get used to the feel and use of the saw, and helps avoid mistakes when cutting the design for real.
Practice until you feel comfortable. Think of the chainsaw like a giant knife. The blade is long and straight. You can curve a chainsaw cut, like you can curve a knife cut, but it is hard to cut a sharp curve with a knife or chainsaw. Also, think of the wood like a stick of butter. A warm knife cuts easily through butter, and your chainsaw will easily cut through the wood. You won't need to exert much force to cut the wood, so focus on keeping your chainsaw steady and your cuts precise. Turn off the chainsaw.
Secure the real wood you plan to carve with sandbags under its sides. Turn on the chainsaw, and cut the design out of the wood by cutting along your chalk marks. Use controlled and steady movements, but take care to only cut where your line is drawn. Use as many straight cuts as possible, as chainsaws are harder to maneuver for detailed curved cuts than other smaller handsaws.
Turn off the chainsaw and move the wood as needed to access other sides, if applicable to your project. Secure the wood with sandbags, turn on the chainsaw and continue to cut along your chalk markings.