TL;DR: Use scan to search for songs using AcoustId fingerprints, use submit to submit unknown fingerprints and generate new AcoustIds.
Yes, the fingerprinting is the basis for the whole AcoustId song identification. What Picard does is as follows:
- If you click scan on a file Picard generates the audio fingerprint for this file. The audio fingerprint captures the characteristics of the recording, but there can be slight differences in the fingerprint of files of the same recording caused by e.g. different encoding or bitrate. Picard uses the fpcalc command line utility provided by AcoustId.
- Picard uses this fingerprint to lookup an AcoustId from the AcoustId server. The AcoustId server will compare the fingerprint and will try to match it to an existing AcoustId. Three posibilities:
a) It doesn't find an AcoustId. The lookup failed
b) The AcoustId server finds an existing AcoustId for the submitted fingerprint, but it is not associated with any MusicBrainz recording. The lookup failed
b) The AcoustId server finds an existing AcoustId for the submitted fingerprint and it is associated with a MusicBrainz recording
- If b) AcoustId is found Picard matches the file to one of the MusicBrainz recordings linked to the AcoustId
If there was no AcoustId found you can use the "Submit" button in Picard to submit the fingerprints to AcoustId server once you have matched the files to the proper recordings. If there was no AcoustId for the fingerprint before the server will generate a new one (which can take a short time). It will also link the AcoustId to the MusicBrainz recording.
So no, you don't need the AcoustId fingerprinting software to generate new AcoustIds. The difference is, that the fingerprinting software is meant to be run on already tagged files, so if it cannot find an AcoustId it will immediately do the submission. For Picard the AcoustId is primarily an identification tool, and as the files are in this step considered untagged you can only do the submission once the files have been properly matched to a MB recording. You will also find that after submission Picard will not automatically fetch the newly generated AcoustIds (the generation can take a short time, and the response we get from the AcoustId server does not contain newly generated AcoustIds). But if you do another scan on the files after submission the AcoustId should be available.