Whenever I forget the syntax for a certain SQL command in Posgres I usually reach for Dash or simply search DuckDuckGo for the the specific command. That usually yields the Postgres official documentation website which is great...
Wouldn't it be nice though if I could stay right inside psql and get the documentation I am looking for?
It would.. and it's possible:
\h create index
\h followed by the SQL command - this is not the full verbose documentation that you would find on the Postgres docs website but it's more of a syntax reference - which is most of the time what you need.
If you are not sure what to type or simply want to explore new commands try typing
\h without anything after it - you will see something like this: