And now it's time for a brief overview of cell phones.
There are two types of phones, basic and smartphone. Basic phones can make calls, text, and some can do basic web browsing and email. Most have a keyboard as opposed to a touch screen. This is a quick way to tell the difference between a basic phone and a smartphone.
The next group is Smartphones. They are devices that generally have more power and can do more, like web browsing, more game, reading, higher-functioning email, etc. The two most popular types of Smartphone operating systems (the phone version of Windows, Mac, etc.) are iOS and Android. iOS is made by Apple, Android is developed by Google. Only Apple devices (iPhones) have iOS, but many manufacturers make Android phones. Most people prefer one or the other. I have an Android phone because of the price, but I have an iPod touch (which basically runs like the iPhone, but doesn't make calls and only works with Wifi, ie, no mobile data) and prefer the iOS operating system over Android. I think it's much more user-friendly.
As a sidenotes, tablets also use iOS or Android in general (minus the Microsoft Surface, which runs Windows). Basically, if it's an iPad, it runs iOS. If it's any other tablet (minus a Surface), it runs Android.
Other types of Smartphone operating systems are Windows Phone and Blackberry. Blackberry is a dying brand. Only time will tell with Windows phones, but they have yet to reach the popularity of iPhone and Android devices (although the Surface is gaining popularity, especially among college students).
As I already stated, only Apple makes iPhones. The most currect devices are the iPhone 6 and iPhone 6+. 6+ is the largest device. There is also the iPhone 5s and 5c. 5c will run you the least expensive, while the 5s will be less (and smaller) than both the 6 and 6+, but still more than the 5c (main difference is that the 5c has a plastic back while the 5s has a metal back).
Other manufacturers make Android devices. Google does make their own devices (Nexus) but most Android devices are made by other manufacturers. Unlike iOS, which basically works across all devices the same, different manufacturers can customize Android, so it's slightly different on, say, an HTC phone as opposed to a Samsung device. Generally, if you get an Android phone, make sure it's a brand name device (like Samsung, HTC, Nexus, Motorola, etc.) as opposed to a brand you've never heard of. If you buy an off-brand device, the quality will be questionable.
This concludes your brief overview of cell phones.