Systemd Homed users and what does 'login' mean?

From homectl:

Home directories managed by systemd-homed.service are usually in one of two states, ... when "active" they are unlocked and mounted, and thus accessible to the system and its programs; ... Activation happens automatically at login of the user

What does 'login' mean? For example, I created a user and tried to su -l test, but I got: cannot change directory to /home/test.

What is required to 'activate' a homed directory if not a login shell?