It depends on whether an ecig is a 2 piece or a 3-piece or a mod
battery + screw on cartomizer
Cartomizer (aka carto) screws on and has limited life (I can get 7-10 days use out of a carto if I keep it damp so it does not singe. If you do not keep a carto damp it will give maybe 10-12 cigarettes worth of drags)
battery + screw on atomizer + press on cartridge (aka cart)
battery + screw on tank atomizer w/ spike + press on tank (and maybe a tank cover)
Fat battery models can have more pieces like an optional outer cone
(note - carts need
juice more often than cartomizers and the atomizer is what can degrade and die, tank carts hold the same or more than normal carts but many end up not liking them. Most use cartomizers for everyday
vaping)
Mods take separate industrial protected or AW IMR batteries which are put inside like you would put batteries in a flashlight.
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I have no idea what you bought. In general using is easy, keeping things damp with
juice is a bit harder than using. Based on the assembled photo yours could be a 2-piece, or a 3-piece of the type where the cart covers the atomizer (RN4081, DSE103, L88b, or other. Less likely it could be KR808D-1 or KR808D-2). And note - some 1-brand vendors call cartomizers "cartridges" but here cartridges are things that use a separate atomizer.