In order to set up trytond you should not need psql.
If you wish to use postgres the server needs to be running, but for development I see that sqlite is usually preferred because of simplicity.
In order to keep things simple I would cd into the tryton-env directory.
If you wish to run from source you should first create an venv:
python -m venv .venv
You should then activate your venv:
Now you should install the necessary components in editable mode (dev mode, from pip install --help):
-e, --editable <path/url> Install a project in editable mode (i.e. setuptools "develop mode") from a local project
This includes dependencies, trytond:
pip install -e trytond
Note that here you need to specify the path to the trytond package inside the tryton-env directory.
After having installed trytond you should be able to execute trytond-admin.
Do note that you need to specify the database in order to initiate it. If you specify -c you need to specify the conf file.
Otherwise you can use environment variables. They are documented on docs.tryton.org.