So, I searched some general tags, and I couldn't find anything. What's the code that one uses to decorate their shop, and can I have some pointers on using it?

Take tags from forum

The tag buttons which are above the field where you type when you post aren't available when modifying the description of your shop, so you have to type them manually.

And by tags I mean, e.g. [B][/B], [I][/I], , [SIZE="x"][/SIZE], etc. etc. etc.