Right hand thumb rule is used to determine the direction of magnetic field around a current carrying wire.
Right hand thumb rule — If we hold the current carrying conductor in our right hand such that the thumb points in the direction of flow of current, then the fingers encircle the wire in the direction of the magnetic field lines.
In figure, the direction of current in the conductor XY is upwards (i.e., X to Y). The magnetic field lines are anticlockwise around the conductor.