NNN/NIS BC bindings use a small clamp that secures a bar at the toe of your boot, while three-pin bindings use metal pins and a toe bail for security. SNS (similar to NNN/NIS) uses a the smallest toe bar and a modified binding plate with a large ridge that runs from toe to heel to help guide the boot.
Your boot and binding types must use the same system. NNN BC bindings work with NNN BC boots. SNS XA bindings require SNS XA boots and are not compatible with NNN. Three-pin bindings work with traditional three-pin duckbill boots or telemark boots.
You can mount three-pin, SNS, and NNN BC bindings on any flat Nordic ski. NNN bindings may also be mounted to skis equipped with an NIS mounting plate. You will just need to make sure that you are using a touring/backcountry XC ski that is wide enough to accommodate the wider backcountry binding.