I've worked at a McDonald's in and it was horrible. The customers were always yelling at you and wherever you work it's filthy. I worked there for most of my 10th grade year in high school and quit cause the pay was so low and it was just not beneficial at all. And sure you get free food but you can only choose a limited amount of itmes on the dollar menu. After a while the food tastes like crap and the smell of burgers make you want to throw up.
On the bright side, I made a few good friends and learned how to operate a cash register. However, I personally would not recommend working at a fast food place. Try to steer clear of big chain restaurants.