We call them "template tags" or simply "tags". These tags being generated withing 4images code and during page compilation they are being replaced by specific content generated somewhere in the code.
There are no tutorials or list of avalable tags, so you kind of will need play with them. Most of the time the tag's name is self explained, I mean, intuitivly you can guess what will be showed instead of the tags...
Also, there is possible use "conditional" tags. These conditional tags starts with {if tag_name} and ends with {endif tag_name}
Whatever is placed betwen these tags will only be displayed if tag_name ( {tag_name} ) is not empty.
The tags being generated through $site_template->register_vars function.
If you see such line in the code, be sure it will generate the tags followed after it.
