After downloading, you can read up on how to get going using our Beginners Guide. There is also a Quick Start reference if you are a more experienced developer.
Included in the download are HTML demo files that can be a pretty good way to try out Galleria without coding from scratch.
Galleria has a large number of options such as transition effects, cropping methods and interaction details that you can use to customize your gallery regardless of what theme you are using. Read through the options documentation for full coverage. In addition to the generic options, each theme has some theme-specific options. Read more in each theme documentation available in the docs.
For the more advanced developer, Galleria exposes an API that simplifies the process of advanced customizations or building your own theme. Read more in the Extending Galleria section and API methods