Hi Emilien,
First of all, did you check that kubernetes is installed correctly? First important step
Pod security policy is defined in a YAML file. This YAML file is then applied, thanks to the kubectl command, in order to define the new policy.
How to create a security policy for pods?
This operation will perform the following operations (via the RunAsAny rule, which is more permissive than the runAsUser option):
- Disable a pod’s ability to run a privileged container.
- Allow the use of SELinux.
- Allow the use of Linux groups.
- Give permission to users to run container entry points with a different username.
- Use of fsGroup will be permitted
To create the YAML file, you have to run the command (you can name the file whatever you want. It must end .yaml):
Learn more: What is a POD in kubernetes ?
Maybe a kubernetes expert could guide us if there are steps missing 
Gianni