Photometry (finding it)
Most coherent, developed, tested materials
Other important CoolWiki pages
Somewhat less coherent (or less standalone) materials
The IRSA YouTube Channel has tons of videos, sorted by tool. There is a standalone catalog search tool, but catalog searches are also embedded in most of the GUI-based most modern IRSA tools. The IRSA YouTube Channel is aimed at professional astronomers, so the videos are very short and assume some background knowledge. They are, however, all closed captioned and can be replayed as many times as needed!