Let's first be clear about that: 5G WILL NOT GIVE YOU CANCER. The radiations used in 5G have lower frequencies than visible light and are thus non-ionising. Even their intensity is too low to cause us any harm.
5G is the fifth generation of mobile communication. With 1G, we could talk to each other. With 2G, we could send messages to each other. With 3G, we could access the internet. With 4G, we had faster internet and could stream videos. With 5G, we have even faster internet and much more.
The internet speed with 5G will be 20 Gbps which is 100 times faster than 4G.
Also, the latency, that is, time difference between uploads and downloads will be 1 ms(4G has a latency of 20ms- our reaction time)
This will enable devices such as robots, self-driving cars, smartphones to connect and communicate with each other faster. This technology will be a revolution is the internet of things. It will be useful in AI. This will give rise to smart cars, smart homes, smart buildings and smart cities.
The way 5G works is that it uses Electromagnetic waves in the millimeter wavelength, that is, a frequency of 24-86 GHz. Unlike 4G, it will be affected by rain and the range will be only a few meters. This means that modems will be installed everywhere. That's a lot of infrastructural work but it will also allow many people to connect at once in a small radius.
The modems are mainly made by Qualcomm and Intel. The infrastructure are made by Samsung and Cisco. This year, Huawei and Samsung are launching 5G phones but I don't think that it will be a success since most of the carriers such as AT&T and Verizon did not installed the network yet. Apple is launching 5G iPhones in 2020.