3G and 4G are known to be mobile data connections that can be used by people when they want to connect to the internet with the use of their mobile devices. 3G is known to be an older type of technology, which means that the speed that it will allow people to connect to the internet will be much slower as compared to 4G, which is considered to be what people use right now.
Do remember that aside from 4G, there is a newer type of technology which is 5G. A lot of the newer phones right now use this. Some people are already trying to decide if they should upgrade to a phone that has 5G connectivity.