The program "postgres" is needed by pg_ctl but was not found

Hello programmers,

I am new to homebrew and I tried to install postgresql on my macbook (mojave) through homebrew : brew install postgresql
But when I try to start postgresql manually: pg_ctl -D /usr/local/var/postgres start

I get this message:
The program “postgres” is needed by pg_ctl but was not found in the
same directory as “/usr/local/Cellar/libpq/11.5/bin/pg_ctl”.
Check your installation.

What can I do to start Postgresql manually?
Thank you for your time.