I'm gonna take it that you aren't pulling our collective leg.
Normally, a modern cell phone uses 4g technology to access data ( and voice ) via cell towers.
The WiFi is an option that will connect your cell to a WiFi connection for data only supplied by you or McDonald's and others to the internet without line charges, and at a muchfaster rate.
The problem with WiFi is the limited range vs the 4g range.
WiFi is usually only reliable within 100 feet of the source receiver/transmitter.