First of all, WI-FI is a wireless local area network and its a form of a technologies that comes from computer networking.

Then, WI-FI was first invented on 1997 and before that people get used of LAN connection but they just created 802.11 that time.

What is WI-FI

• Firstly, Wi-Fi and its known as wireless local area network 
• Its actually work using radio frequencies to deliver signal to the devices.
• After that, when WI-FI created on 1997 and they used on cellphones, walkie-talkies.
• Wirelessly transmit network to their devices and its trademarked as IEEE 802.11x.

How its works

• As well as, WI-FI first used in computer and its works from computer by a wireless adapter
• Translates data to a radio signal and transmit it using antenna.
• Not only that, the wireless network receive signal and decode it
• Send information to internet using a wired ethernet connection.

Do we need modem to use WI-FI?

Yes, but if you want to use internet u need to use modem for internet access and without internet u can use WI-FI to transfer data to another computer or smartphone.

As a conclusion, this is what is WI-FI and how its works actually and not only that if you wish to have high speed of internet have a look below u will get your internet as you wish.