I've been trying to use the variables of HP to run it so whenever (after attacking someone) that person loses all their HP, they're taken to... a hospital, or someplace like that. However, I don't know how!

Each time the player is attacked you can use a condition to check if the player has equal to, or below 0 hp. Something like the following should be added to your attack procedure (If you have one that is).

if ( %hp% <= 0 ) then goto <Hospital> else ' do damage procedure

Oh, also make sure you use the correct variable format, otherwise it won't work properly. Something like, %hp[id]% or some crap like that.