Because there is always a risk when streaming, I will include a link for the VPN that I use here.
An Android box, or a TV box or Kodi box, is essentially a user friendly, compact personal computer specifically made for a seamless experience on your HD TV. It can be attached to any TV with a HDMI port instantly transforming your TV into an Android Smart TV. They are very versatile and powerful little devices, capable of playing media (video or audio files) from local storage (USB flash drive, USB hard drive or SD card), a NAS (Network Attached Storage) device or via the web through a browser or media center such as Kodi (formerly XBMC).
You can also install apps and games from Google Play Store (free and paid), surf the web, browse YouTube, watch your favorite shows on Netflix, Crackle or PlutoTV, listen to your favorite jam via Google Play Music, check your local weather in just a click or tune in to your local radio station via TuneIn Radio. Check out all the software titles available at the Google Play Store.
So when you purchase an Kodi box it's most likely an android box that has the Kodi app installed.
All you need is a high speed internet connection! Ideally a speed of 10 Mbps (equivalent to 1.25 MB/s) or more is best. 5 Mbps will work but you may experience freezing/buffering with high quality streams.
With the ever increasing, physical, size of apps these days it is recommended to have at least a 2GB android box with the latest version of android as possible. Get the latest gear here.
Many apps do have backwards compatibility, but the are limits. For example: Android 4 does not support Kodii 17+.