To install the photoalbum-module, just unpack the flatcms_photoalbum package to your flatcms directory,
create directories beneath /data/photos/, one for eatch photoalbum category (or album) and copy your images to this directories
Captions can be created with the Admintool. You can also create a textfile with the same name as the imagefile (like Photo1.txt for Image Photo1.jpg) and write your description into it.

have fun with it.