A Turing machine is a mathematical model of computation describing an abstract machine that manipulates symbols on a strip of tape according to a table of rules. It is capable of implementing any computer algorithm.

To create a Turing machine, first enable state mode and draw mode. Then, click on the canvas while state mode is enabled to create states, and draw edges between states while draw mode is enabled. You can define transitions by clicking on the edges. To start the machine, select a start state, an accept state, and a reject state. Note that the reject state needs to be created even if it won't be used in your Turing machine. This ensures that symbols with no transitions at particular states automatically go to the reject state.

If the simulator reaches a state and no transition is defined for a particular symbol, the input is automatically rejected. You will be notified that a transition was not defined. This means you can leave out transitions to the reject state, making your Turing machine diagrams neater.

Yes, every Turing machine graph needs to have a reject state defined, even if it won't be used. You can simply create the reject state without defining any transitions to it. This is so that symbols with no transiions at particular states go to the reject state.

The blank symbol is a special symbol that represents an empty space on the tape. It is used to indicate that a cell on the tape is empty. The blank symbol is denoted by the underscore symbol (_) on DrawTurings.