What does the operator selection setting on a smartphone give?

Question

mobile connection

If in the network setting, the operator selection value is set manually, when the smartphone is turned on, a list of available operators is displayed. If you choose a "foreign" operator, but being in the "home" region, then what will happen? When can another operator be used? What will be the payment?

Answer 1

You will just be roaming.
Tariffs can probably be found on the website of your operator.
Well, when there is no connection with your operator, but you really need it and money is not a problem, then why not.