“You shall utterly destroy them!” (Devarim 7:2)
It is a positive commandment to kill the seven nations who took control of Eretz Yisrael before we conquered it from them, and to destroy them wherever they are to be found, as it says “You shall utterly destroy them!”. (These nations are the Canaanites, Emorites etc.)
Amongst the roots of this commandment are that these nations had commenced to serve idols and commit many sins which are abominations before Hashem and He hates, and since they are the basis of idol-worship, we are commanded to annihilate them from under the heavens, so that they will not be remembered or mentioned in the land of the living. By doing this we will achieve that we will not learn from their actions. We can also take a lesson from this, not to move towards idol-worship.
One may not ask “Why were these evil nations created, when their end is to be annihilated from the world?”, as we already know that every person has the power to choose to be good or bad, and Hashem will never force a person to be either good or bad, and at the beginning of creation these nations could also have chosen to be good. They did not take their chance and damaged with their deeds and became evil, to the extent that they all deserved to die.
This commandment applies both to men and to women, in all places and at all times that we have the power to kill them. Even though in actual practice it is impossible to perform this commandment, as King David already did it by destroying them until there were so few remaining that they were scattered and assimilated into the other nations so that no memory rests of them, and we can no longer chase them and kill them, the main commandment is not bound by time, and always applies.