I believe they're just point and shoot. It fires a laser which measures the heat given off of a surface. Point it at the spot you want to measure, observe the reading on the digital display.
They're pretty expensive though, personally I wouldn't buy one unless I had multiple enclosures. I just use a digital thermometer with a probe.
thats it. most are one button point and shoot. just understand the spot ratio of any given temp gun. the higher the ratio, the better. for example a 10:1 ratio means if you hold your gun 10 inches from the surface you are temping, it will read a 1 inch circle. the cheaper the gun, the lower the ratio will likely be. like the pro exotics pe1 is a 1:1 ratio...so if you hold the gun at ten inches, you are reading a ten inch circle. the pe2 is like a 6:1 ratio, and cost around fifty bucks. this is the one i use now, i have used very expensive ones, and i am just as happy with my pe2. in my opinion, they are the most valuable tool a herp keeper can have, unless you keep venomous, then i would say hooks and tongs, but that is another thread.