It all begins simply. First, you make a magic wand. Second, you right click on a bookshelf to receive the Thauminomicon (basically a guide to the mod). Next, you build a research table and a thaumometer. The thaumometer lets you scan blocks and items in the world. That will give you 'research points' which you use to conduct research and discover various magical creations that you can make.
In order to actually do any magic, you will need to find various aura nodes that are scattered throughout the world. Normally, the are very faint spots of light that are difficult to see. However, if you are looking through your thaumometer, they will be reveal as small glowing stars. You can use your wand to drain energy from them (called vis) which you can then harness to do various magical things.
|Aura node as seen with the naked eye|
|Aura node seen through a thaumometer|
|Aren't golems cute?|
Overall, it's a really fun mod. It can be difficult to troubleshoot why things aren't working, but the end results make me feel like I've accomplished something. Personally, my favorite part of the mod is creating farming golems and a wand focus that lets me shoot lightning like I was a Sith from Star Wars.
I've done a short video sort of highlighting a mod. Hope you enjoy!
If you're interested, more information on the mod can be found here.