This article covers how to use Snap and how it updates. Snap packages are set to refresh (update) 4 times per day by default.
It should also be noted that automatic updating of snap packages cannot be completely disabled directly from the snapd settings, as there's no option for this (what's up with that?), so if you want to disable this altogether, you'll have to resort to workarounds like blocking the snap update URL, or setting your Internet connection to metered and them using the refresh.metered option to hold the snap refresh process when a metered connection is detected (sudo snap set system refresh.metered=hold).
If you want to check if a certain snap is available from the snap store, use the syntax:
$ snap find [ package name ]
To view the current snap refresh (update) schedule for your system, use:
# snap refresh --time
To change the snap refresh schedule, use:
# sudo snap set system refresh.timer=<frequency>
You'll need to replace <frequency> with the snap refresh frequency you want to set for the timer, as defined in the Snapcraft documentation.