Trusses belong to structures which are extensively applied in various civil engineering applications like bridges, steel buildings and roof structures.
The method of joints is the most recognized process to discover unidentified forces in a truss structure. Under this process, all forces functioning on a joint must add to zero. If there exist a net force, the joint will shift. When a truss remains in equilibrium, then each of its joints should be in equilibrium. The method of joints comprise of satisfying the equilibrium equations for forces working on each joint.
Go through the following video, to get the detailed process.