The most basic two way radio systems are simply those, which utilize one or more handhelds, and possibly an extender to provide more coverage. The need for an extension is based solely on the distance your handhelds are required to cover, so only those communicating in a larger area will actually need this extra assistance.
Handheld radios can communicate with each other very well just on their own. The antenna, which screws into the top of the radio(s) allow for this coverage. Some radios come with stubby antennas and some with long-whip antennas when you purchase them. If you are working with stubby antennas and still need a little bit more coverage, then switching to a long-whip might just be the proper solution for you!
Sometimes switching antennas may not get the job done, and you may require a coverage extender such as a repeater. Repeaters are available in order to provide this extra coverage for your system. It simply catches signal from the sending handheld and throws it twice as far to reach the receiving end. It is a fairly simple process, which gives a basic system a bit of a boost.
So, whether you require simply a few handhelds or if you utilize multiple radios along with a repeater, these are still considered basic radio systems.
If you are interested in learning more advanced radio usage techniques and options, feel free to stop by the Two Way Direct YouTube page: https://www.youtube.com/twowaydirect