Actually, at least in Europe, it is not uncommon for the instructions
to say "type [name of router] into your browser". I guess what happens
is that the router is the DHCP server of the computer connected to it
and this name resolves to some IP address.

Standard seems to be 192.168.1.1, though other 192 addresses are sometimes
used.

A feature of the Fritz!Box I like is that it has one rather unorthodox 192
address which cannot be changed, so that is always there as a back door.
There are one or two other 192 addresses pre-configured, but these can
be changed. The browser menu also has an "expert" button. You can do
stuff like change the IP address only if the "expert" functionality is
enabled, otherwise such things don't even show up in the menu.