I think the best thing to do is not worry about what mo
st other distance runners do, only because you are in HS and cannot really argue with your coach. I can understand your concerns as an athlete though. Before I give you a few answers, you should know that you also need to go back to your coach and ask him/her all of these questions. They should be able to give you valid answers for their own training they are prescribing. It's perfectly ok to question a coach in terms of learning about the benefits and expectations from your workout. You aren't challenging his authority that way, you are simply trying to educate yourself on what you are doing. Quite frankly, he should be explaining this to your entire team. They will be more likely to be motivated and adhere to the lifting that way.
To answer some of your questions, no not all runners lift heavy weights. He is most likely having your find your 1RM in order to prescribe what weight you should be lifting for each lift. You shouldn't be doing RM lifting on a regular basis.
Also, every runner is going to give you a different opinion. Some are advocates of lifting and some are not. Many distance runners believe it makes them too tired for their runs and workouts. Others love it and believe it makes them stronger and prevent injuries. I happen to love lifting as a supplement for my running; however, I wouldn't prescribe it to everyone. It's not FOR everyone. Every individual is different. One of the biggest challenges a HS coach faces is being able to treat athletes on an individual basis; it just doesn't happen. You are going to be treated as a unit because most HS coaches do not have the time or resources to devote that much attention. Also, most coaches do not have degrees in physiology or kinesiolgy; they aren't always going to know the BEST thing in terms of training. This isn't to knock your coach or anyone else's.
Anyways, to makes the most of your coach's training..
One suggestion would be to lift after an aerobic run. If it's your long run that is ok but you will obviously feel more tired than if it was a normal run of say 45-60 mins. However, the main focus of your training is running so if you cannot always feel good during your lifts that is ok. You are still receiving benefit.
Secondly, lifting burns a LOT of calories. If you are lifting directly after a run EAT before you lift. It doesn't mean you need an extra 2,000 calories a day. But you should be properly fueling yourself so your body can handle the work and recovery. What I would do is buy a chocolate milk to have after your run. It's a great ration of protein:carbs:sugar and will help your muscles recover from the run and also give you energy for the lift. Also, eat something again after the lift. I always bring a small yogurt and a banana. It's healthy carbs and a small amount of protein. Trust me, modest but proper fueling is going to make a world of difference.