@c5bffeca for Infinity, it’s stats + mods.  So my heroic Nomad Alguacile will shoot, with a BS of 11, will shoot at your perfidious PanO Fusilier, who will dodge with a PH of 10.  I’m in good range (+3 to me) but you’re in cover (-3 to me)… but I’m behind you (-3 to you), so all said and done I’m rolling for an 11 (but not higher!) and you’re looking for a 7 (but not higher!) on d20s. I’m Burst 3, so I’m rolling 3 dice and you’re rolling 1. 

 @c5bffeca I roll a 14, 8, and 5.  You roll a 6.  My 14 fails. My 8 is higher than your 6, it’s a hit! My 5 is lower than your 6, so even though it’s a successful result, you dodge it.  

A million variations: critical success when you hit the target exactly, automatic successes when your target is >20, etc, but it’s fundamentally a very simple system.