Why roads on hills are narrow and winding?
It is less expensive to cut through a small portion of a mountain than it is to remove the entire thing plus it looks better and the winding is because it is better to wind around than go straight up and down.
How to improve my biking enderance and uphill skills.?
It's amazing how much you can lose in a short period of time, after taking a year off it will just take time to get back to where you were. Be persistent and in a short time it will get easier. Once you get to the point where you can top the hill work on doing it faster. A fun drill (if your into pain) is to ride up the hill till you are a few hundred feet from the top then get out of the saddle and pedal like a rabid dog is chasing you. One key, use your gears to your advantage, downshift early, waiting till you need the gear will only fatigue you and once you reach that point it is very hard to recover on a climb.