Users Registration in static page.

Hello,

I want to ask, how to make users registration and login in the page inside but not in the different page.

For example: https://mydomain.com/register, i need that when i will go on this link would be a user registration. The real example is:

https://ikrauk.15min.lt/registracija (This link is for user registration)
https://ikrauk.15min.lt/prisijungti (This link is for user login)

Another example: https://smartsavingsusa.com/register/

Or what plugin do they use?