The Maxwell's right hand thumb rule states that “ When the conductor is held in your right hand, such that the direction of the thumb points the direction of the current and the curled finger gives the direction of the magnetic field. ”

For example, if the current flows upwards through a vertical wire, and you position your right hand with your thumb pointing up (in the direction of the current), your fingers will curl around the wire in a counterclockwise direction. This indicates that the magnetic field lines are oriented in a counterclockwise manner around the wire.

Hence, Maxwell's right-hand thumb rule shows the direction of the magnetic field produced when an electric current flows through a straight wire.