First game ever was a parks & rec game with 8-9 year olds that my wife talked me into doing with her. I remember that I wore black sweat pants, a collared striped shirt, and big metal framed glasses. My wife laughs at me to this day, saying that she doesn't remember me blowing the whistle at all. I just remember being very nervous - trying not to make a mistake and prove to everyone I didn't have a clue (which I didn't).
I continued to do games at that level for the rest of the season, giving my first technical foul to a coach who's son got a foul call for using his arm to push off his defender while he was dribbling the ball. He told his son I didn't know what I was talking about, and to just keep doing it.
My first high school game was a jv girls game at a school very close to my house. I was just as nervous as the first game mentioned above, but had a little more rules knowledge. I don't remember much about the game except the play seemed extremely fast and I struggled to keep up with it.
My first partner at that game was great! He always smiled and very gently guided me in the right direction. I'm sure he covered quit a few of my mistakes. I will always be appreciative for that and vowed to remember to treat new officials the same way he did me.