Is it necessary to wash clothes before or after performing ghusl for janabah, and do things become impure by coming into contact with one who is in a state of janabah?

A Muslim never becomes impure, even if they are in a state of janabah (definition) (major ritual impurity). What a Muslim touches while in a state of janabah does not become impure, unless their hand has impurity on it and that impurity transfers to the touched object. As for clothes that have been touched by impurity, they do not need to be washed unless the Muslim intends to pray in them, in which case only the impure spot must be washed, not the entire garment.