Shots are pretty easy to explain. It's like calling intiative in D&D, except everyone goes every 3 numbers (usually.) When a fight starts the players determine their initiative; have them put a paperclip or something on the number if you number the edge of their character sheet 1-20. Then you start going around the table. To be fair, I usually go clockwise, then counter-clockwise, the clockwise, bouncing back and forth around the table. 18 (look in turn at each player)... 17 (look in turn at each player)... 16. "I go!" says the player who goes first. Then, so long as he's making normal attacks, he goes on 13, 10, 7, 4, and 1. If he does something that has a shot cost of 1, like (iirc) reloading, it slides all those numbers down one.
Sounds confusing, but it goes quickly once you get the rhythm. Put pencil marks on your own chart to note when the bad guys go.