+1 on hairballs post... some last longer than others... depends on how you vape and with what fluid. I always recommend the "atty resurrection method". Do a search, you'll find the post. When my attys get gunked up, this cleans them to like-new condition!
Clearer liquids are easier on attys... and liquids with high/all VG content are rougher on attys.
To answer your question, atty/carts are labeled by their threads (what they'll screw into). Every E-cig will always tell you what threading it will take. Threads are numbered... 510 is very popular, but others include 901, 801, etc.
As long as the threads on your atomizer/cartomizer are the same as what your e-cig takes, you're in good shape. Cartomizers are just a different method of liquid delivery and vaporization. They are a heating element and juice-holding foam in one! Some find that cartomizers require less maintenance and allow longer vaping sessions... but they dont deliver quite the vapor that a traditional atomizer paired with either a cartridge or drip-tip can.
Some companies make thread adapters, too. For example, If I wanted to use a 901 atomizer on my 510 device, I would need a 510-901 adapter.
I also highly recommend a "fat battery" 510 mod like the non-tank ego/riva/inferno/tornado. Those are all basically the same thing, just different brands. To further clarify, those model E-cigs will accept 510 cartomizers/atomizers.... or any other cart/atty with the proper adapter!