You are lucky in a way that OMV has a fantastic documentation suite. it is not too long, and I recommend reading it cover to cover, as well as the omv-plugins and omv-extras documentation, skipping over anything that’s not interesting, but seeing that it’s there for future reference.

OMV is interesting to me because it gives you a gui that lets you do many difficult or advanced things fairly quickly, but it is not always clear what all the options do, and things don’t always work as expected. My advice is start slow, stick to the garden path (don’t try anything custom or unusual), and frequently browse the forums.