Every vape uses some kind of heating element to atomize vape juice, and whether it's in a pod or a tank or whether it's wire or mesh, it will need to be replaced when it wears out. Vape coils are almost always device exclusive, meaning your vape uses a specific type of coil and won't work with coils designed for other vapes. Once you figure out what kind of atomizer you need for your vape, you will often still have a few options to choose from. Most vapes have several different coils available that will provide a different experience. The most common variable between coil types is resistance.
To use the Kangertech Evod as an example, you can choose from 1.5 ohms, 1.8 ohms, 2.2 ohms or 2.5 ohms. Generally speaking, a lower resistance vape atomizer will provide more heat and vapor production, where a higher resistance atomizer will be cooler and produce less vapor. You may have a choice of coil materials as well. The most common resistance wire that's used to make vape coils is Kanthal, which provides good heat and flavor. NiChrome is also somewhat common and behaves similarly to Kanthal, though it often provides better flavor. Coils made of Kanthal or NiChrome are rarely labeled as such, so if your coils don't specify, they're likely one of these two materials. Stainless Steel is also becoming very common, with most vape companies offering some kind of SS316L coil which can be used in either wattage or temperature control modes.
Less commonly, you might see materials like Nickel, Titanium or other Stainless Steel alloys. Nickel and Titanium are to be used exclusively in their respective temperature control modes, and we recommend that you only use temperature control coils if you know how to use them. For some companies like SMOK, resistance and coil material are largely irrelevant, and the focus is on the physical design of the coils. SMOKtech offers many different coil types for each of their vape tanks, from standard single core coils like the Q4 all the way up to something like the T10 coil for the TFV12 Prince, which has five cores. Regardless of what your options are, it's usually best to experiment with different coil types to find one that suits your taste and vaping style.