sqlplus sys/oracle@orclcdb as sysdba;
Alternative:
sqlplus system/oracle -> this will login to pdb
alter session set container=cdb$root ->this will change it to cdb

sqlplus system/oracle -> this will login to pdb

show con_name ->if this shows cdb$root then you are at cdb otherwise you are at pdb

Just type “clear” to clear your command line screen. When you take screenshots, this will look useful because you can delete the SQL commands that give you an error before taking the perfect correct and simple screenshot that your instructor always wanted.