Knowing the direction of the current, it is possible to determine the direction of the magnetic field using Maxwell's Corkscrew rule, usually abbreviated to the Corkscrew Rule (or sometimes the right hand screw rule). The Corkscrew Rule states; if a corkscrew is turned so that it moves in the direction of conventional current flow, then the direction of rotation of the corkscrew corresponds to the direction of the magnetic field, see diagram below.
Attraction & Repulsion
Two parallel wires, which are close together, each carrying an electric current, produce magnetic fields which interact with one another. If the currents flow in the same direction, the wires experience a force of attraction. If the currents flow in opposite directions, the wires experience a force of repulsion, see diagram below.
The force between two such conductors forms the basis for the definition of the unit of current - the ampere.