Purchase and download section property channel software. You can find it through a number of engineering sites or by a simple web search. Property channel software is much more efficient and accurate then hand calculations.
Choose a shape or structure that you would like to section. Generally, channel sectioning is done for more complex shapes.
Measure or determine all of the different aspects of the shape you are using. You will need measurements such as area, side lengths, velocity, radius, angles and other dimensions.
Submit your measurements to find the following possible channel section properties:
Area
Moment of inertia
Radius of gyration
Center of mass
Plastic section modulus
Shape factor