In otherwords say you want to login as sysdba then you just do this:
sql / as sysdba
And you get the following:
[oracle@ol8-19 ~]$ sql / as sysdba
SQLcl: Release 21.2 Production on Thu Sep 23 17:37:51 2021
Copyright (c) 1982, 2021, Oracle. All rights reserved.
Connected to:
Oracle Database 21c Enterprise Edition Release 21.0.0.0.0 – Production
Version 21.3.0.0.0