Hi Joan,
Good question :)
The activeScan-policy job allows you to configure an active scan policy. It does not actually do any scanning.
The activeScan job performs the active scan. It allows you to either use a build in policy, a policy thats been created by the activeScan-policy job, or one thats specified "inline".
We also have a sequence-activeScan job which allows you to active scan sequences.
If you want to perform any active scanning then you have to use either the activeScan job or the sequence-activeScan job.
You do not need to use the activeScan-policy job, but you may find it useful, especially if you want to use the same policy for both jobs.
Does that make sense?
Cheers,
Simon