The purpose of this model is calculation of reactions and internal forces of tension or compression in truss members of statically determinate 2D trusses with arbitrary number of joints. All joints are supposed to be hinged. The external forces and reactions (the amount of corresponding constraints must be equal to 3) can be applied at arbitrary joint, but should be represented by their horizontal and vertical components. The method of joints is used in the calculation. It is helpful not only for structural engineers, but also for students because all main steps of the solution are provided.