'To cast' in this context means 'to throw' forcefully - so the author is trying to communicate that the people were forced into darkness. It's quite an old fashioned, biblical term.

I think that they should teach us about basic farming. This would have two impacts on/benefits for us. Firstly we would be able to produce food that we eat regularly and, secondly, it would connect us to our land.

Hi! You could actually use it in both ways. In the case of healing someone or making them feel better we usually refer to an object or a general action 'putting somebody right' as opposed to a person doing so , e.g. "A good night's sleep will put you right." In terms of the second meaning, yes, it means to correct somebody - particularly where that person has got some facts wrong, e.g. "Actually that's not quite what happened, let me put you right about a few things." The second meaning is used more commonly.