I'm a huge Stylebook fan, and have been using it for almost four years!
Yes, getting started can be daunting, but there is no need to do it all at once. As mentioned, start with the outfit you're wearing. Save photos of anything you buy on line. then do small photo blitzes... a pile of sweaters one day, white tees another. Make sure you photos things on a background that is consistent and a totally different colour then the items, it makes it much easier to edit the photos within the program.
I use it for all kinds of things that it's not really designed for. The packing list feature is especially useful. One of my off-the-wall uses: at the beginning of a season, I'll make a packing list called "tops not worn spring summer 2018". I'll "pack" all the tops I MIGHT wear in that season, and delete them as I actually do. It's so easy to see what you are not reaching for... should reach for... or should get rid of. When doing my 30x30 challenge, I "packed" the outfits, so I could easily see what numbers I was at and what I'd chosen. As the days went on, I looked at the packing list to see what I could choose from. (obviously there was more planning than just this, but it was an easy visual)
The new "style stats" features are awesome.
It's not perfect, but it's pretty darn good.
I echo Roxanna's recommendation to search here for threads to see what people have to say about it, and how they use it.