Download Oracle Database 18c from below link.
https://www.oracle.com/technetwork/database/enterprise-edition/downloads/oracle18c-linux-180000-5022980.html
Login as oracle open terminal
Unzip software
[oracle@oraclehost ora18c] $ unzip LINUX.X64_180000_db_home.zip
https://www.oracle.com/technetwork/database/enterprise-edition/downloads/oracle18c-linux-180000-5022980.html
Login as oracle open terminal
Unzip software
[oracle@oraclehost ora18c] $ unzip LINUX.X64_180000_db_home.zip