I Live In The State Of NY. Yesterday, My Physician

I live in the state of NY. Yesterday, my physician prescribed Sudafed. When I purchased it, it was behind the counter. I had to show an ID. Someone told me kids abuse it.

Two questions: What are the kids doing to abuse it. It looks innocent enough.
If I run out of these, am I able to go back and purchase them? I am having a lot of trouble with congestion and am a flight attendant. I need to get my sinuses and fluid filled ears cleared up quickly so that I can fly again. Thanks.