connect to Oracle Cloud from SQLPlus and Instant Client
Assuming your Oracle database on Oracle cloud then you can connect to SQPLUS over SSH:


connect to oracle cloud service
click on the name of the deployment you want to connect to
copy public IP address
switch to Linux command prombt
check your and confirm the private public key for your deployment exist
run ssh -i ua_key_openssh oracle@IPADDRESS_YOU_GOT_FROM_POINT3
execute sqlplus command 
enter username\password