It varies. Secure routers don't have WPS. The routers with WPS may have the button anywhere where it can be accessed relatively easily. Some may rely on a PIN number.
Since WPS has a significant security weakness, if the router has the facility to completely disable WPS, for you network safety you should disable it.
For WPS to work, both the router and the connecting device must support it. Many devices do not use WPS, and as each device only needs the pass phrase to be entered once, you might as well get used to typing the character string. It doesn't take very long to do.
I hope this helps.
Not all routers have a WPS button. The ones that do, it could be on the top, side, front or back. NEVER on the bottom. Which router??
Depends on if your router has one to begin with.
it is a fast way of allowing devices to join the network without the code
if a device has WPS you turn it on on both devices and wait