Using a matching function. As this suggests, it is also helpful to have an explicit or implicit failure state . Typically, we represent finite automata pictorially. Each state is represented by a circle. The transition function, delta, is represented by directed and labeled edges between states.
Final states have a double circle.
The start state has an incoming arrow. Sigma is not represented explicitly. You may find it easier to represent some tokens with finite automata and others with regular expressions. However, they have the same computational power. Typically such edges are labeled with epsilon.