These kits include mod and tank, not always including batteries. They are aimed at the more advanced vaper. If you are looking for something more basic or are a beginner then look at the starter kits here.
Advanced kits are aimed at the user who has had some experience with using an e-cigarette. Typically these are Sub Ohm devices and are classed as straight to lung, STL (or direct to lung). When you vape STL you produce huge amounts of vapour, commonly know as cloud. This type of product usually use power in excess of 50Watts, and in some cases, if your brave enough, well over 300Watts. You will also get features such as variable wattage, temperature control, and in some cases even an MP3 player built in.
OK so why do you want to vape like this? Well most people get a large amount of satisfaction from from STL vaping and there are a huge amount of e-liquids aimed at this type of vaping. Shortfill e-liquids are the usual type of juice that Sub Ohm vapers go for. This is because they are not regulated, so are in larger bottles which gives you better value for money than 10ml TPD bottles of e-liquid. Typically a Sub Ohm vaper will use shortfill bottles, called this due to the bottles not being full so that you may add your required amount of Nicotine liquid after you purchase.