Not sure what you mean, are you asking the difference between regulated and unregulated devices?
Regulated devices have variable wattage and variable voltage - Sometimes (not all the time) they have an internal battery, but other times you need to get an 18650 battery for it, the advantage to these is that you can control the amount of wattage or volts going to your atomizer, allowing you to find a nice sweet spot, and the vape you experience is more constant, but the downside to this is a lot of them are limited to a certain power (50W, 60W, etc) but there are a few that go up to 100W/200W which is plenty.
Unregulated devices (normally) use 2 18650
batteries, there are two types of these, series and parallel, parallel being the most common. With these devices you get the voltage of the
batteries applied to the atomizer (if it's in parallel, the voltage is "shared", but with a series box mod, the voltage is combined, so both the batteries voltages, i.e 8.4v instead of 4.2v in a parallel - fully charged) with these unregulated devices, people prefer them as you can achieve high wattages.
There is a lot to consider and research when it comes to this, hopefully I've just scraped the basics.