Systemd service life cycle

[Colin Law]

I am trying to define the startup order of a couple of systemd
services.  I see in the docs how I can use After, Before etc to
control the order.  What is not clear to me is at exactly what point
in the startup of a service it becomes "Started", thereby allowing the
next service to be started.  I have tried looking in the docs and
googling but have not found the answer.  I am sure it is there in the
docs, but there is quite a lot of it, so if anyone can save me some
time I will be very grateful.

Cheers

Colin