Welcome!
Basically you have to download the script and install it on either a webhost (for public use) or WAMPP/XAMPP (for personal testing/prototyping). There are a few tutorials here on installation, but I recommend following
this one, regardless if your using a host or WAMPP. It worked better for me than the official tutorial, and it's updated for 1.3.4. Also make sure you apply all of the fixes listed
here if you want to avoid running into those issues later.
Once you've finished installation, you have the ability to upload different images for your pets through the ACP (admin control panel) -- an egg image, level 1, level 2, and level 3 (though it is possible to add more levels). Right out of the box, the script allows you to make something similar to dragcave where an adoptable earns a level after getting so many clicks, and users are able to use the generated codes to put in their signatures and whatnot to help earn those clicks. Here's also what's available by default:
- Breeding and creating breed-only adopts that can only be obtained through breeding, rather than a shop
- promocodes, which can be used for items or pets
- trading, although it could use some refinement
- item shops and pet shops
- an admin control panel, for managing site settings, users, pets, shops, and items.
If you want to add more features, you either make them yourself or look in the "mods and addons" board or the "tutorials and tips" board.
You can ask if anything else isn't clear.