What does it mean to construct viable arguments and critique the reasoning of others?

It means that you are using your intelligence to examine your thinking and that of others to see if it really makes sense. "Viable arguments" are ones that make sense, that are connected in a logical and practical way, and are not just an appeal to the emotions. E.g. "These poor children are starving, therefore give money to me." (The logical and practical response is that since the children are the ones that are starving, the money should go to them, not the internet huckster. This should lead you to find out how best to get money to the children.)