Is WIFI like a hub, switch or router? A wireless router; the wireless part of it, is that a layer 2 or layer 3 device? I have heard that a WiFi router is just a wired router with a built-in wireless AP, and since a wireless AP functions as a hub or switch, then there is no added benefit other than simplicity for buying a WiFi router vs buying a wired router + a wireless AP? Also, I have heard that wireless APs functions like a hub and a switch at the same time. I am really confused. How does a wireless AP work compare to switches, hubs, and routers?

A WAP is like a hub on the wireless side, and a translating bridge (a switch is a transparent bridge) between the wireless and wired side.

Routers route packets (stripping off the frames and building new frames) between networks. Bridges bridge frames on the same network.

What most people call wireless routers are consumer-grade devices (off-topic here) that are Frankenstein boxes and have multiple devices in the same chassis.