1、sqlplus里面的命令用help，例如

SQL> help connect

CONNECT
-------

Connects a given username to the Oracle Database. When you run a
CONNECT command, the site profile, glogin.sql, and the user profile,
login.sql, are processed in that order. CONNECT does not reprompt
for username or password if the initial connection does not succeed.

CONN[ECT] [{logon|/|proxy} [AS {SYSOPER|SYSDBA|SYSASM}] [edition=value]]

where logon has the following syntax:
username[/password][@connect_identifier]

where proxy has the syntax:
proxyuser[username][/password][@connect_identifier]
NOTE: Brackets around username in proxy are required syntax

SQL*Plus® User's Guide and Reference

https://docs.oracle.com/en/database/oracle/oracle-database/21/sqpug/sqlplus-users-guide-and-reference.pdf

2、操作系统级的命令，一般用-h  --help  help等参数，例如

srvctl -h
Usage: srvctl [-V]
Usage: srvctl add database -d <db_unique_name> -o <oracle_home> [-c {RACONENODE | RAC | SINGLE} [-e <server_list>] [-i <inst_name>] [-w <timeout>]] [-m <domain_name>] [-p <spfile>] [-r {PRIMARY | PHYSICAL_STANDBY | LOGICAL_STANDBY | SNAPSHOT_STANDBY}] [-s <start_options>] [-t <stop_options>] [-n <db_name>] [-y {AUTOMATIC | MANUAL | NORESTART}] [-g "<serverpool_list>"] [-x <node_name>] [-a "<diskgroup_list>"] [-j "<acfs_path_list>"]
Usage: srvctl config database [-d <db_unique_name> [-a] ] [-v]
Usage: srvctl start database -d <db_unique_name> [-o <start_options>] [-n <node>]
Usage: srvctl stop database -d <db_unique_name> [-o <stop_options>] [-f]
Usage: srvctl status database -d <db_unique_name> [-f] [-v]
Usage: srvctl enable database -d <db_unique_name> [-n <node_name>]
Usage: srvctl disable database -d <db_unique_name> [-n <node_name>]

3、Oracle® Database SQL Language Reference

https://docs.oracle.com/en/database/oracle/oracle-database/21/sqlrf/sql-language-reference.pdf

4、Oracle® Database Database PL/SQL Language Reference

https://docs.oracle.com/en/database/oracle/oracle-database/21/lnpls/database-pl-sql-language-reference.pdf

show parameter 参数名