Simple knockback in 2d sidescroller. Vectors?

I`m trying to make simple 2d sidescroller game. And now my problem is in pushing enemies or player in opposite direction of instigator. I cant find any tutorials about it, also I tried to make it by myself, but I don’t understand how can I get a direction vector
Also I m not sure is it right to use launch character for this action.

Any help is appreciated!