Where do we set the initialization parameters?

Where do we set the initialization parameters? Is this in init.ora or spfile?
Is this where we have to set the location parameter for ADR?

There are two common ways to find out to what value an initialization parameter is set:
show parameter <param_name> in sql*plus, or
select value from v$parameter where name = lower('param_name')
The parameters can be changed for the currently connected session with a alter session set ... command.
If a parameter should be set in another session, dbms_system.set_bool_param_in_session or dbms_system.set_int_param_in_session can be used.