First, I have selected and resized 299 images from my photos, and I copied them into the /img/ folder of my blog.
Then, I made thumbnails for the images in order to optimize the site. (These steps can be done in bulk with your favorite image editor.) Thumbnails are tiny versions of the pictures, with a thumbnail - prefix.
Then I made a html page skeleton, referencing
JQuery (necessary for Galleria)
the Galleria classic theme css file
my custom script
The html body contains only one div, with a galleria class. We will use this div to display the images with Galleria.