Two parallel conductors $1$ and $2$ carrying current $I_{1}$ and $I_{2}$, respectively of length $l$ is shown in the figure given below,
Force on wire 2 due to $B_{1}$ is given by
$F_{2}=I_{2} l B_{1}$
Using right hand screw rule, direction of $F_{2}$ would be towards wire 1 .
Similarly, force on wire due to $B_{2}$ (field of wire 2)
$F_{1}=I_{1} l\,B_{2}$
Again, by using right hand screw rule, direction of $F_{1}$ would be towards $2 .$
If two parallel conductors carry (equal or unequal) current in same direction, they will exert force towards each other i.e., they will attract.
However, if these parallel conductors have current in the opposite direction then they will exert force away from each other such that they would repel.
