How to rename files based on tags?
Renaming files, creating folders and complete directory structures from tags can be done by using the 
Converter > Tag - Filename with a format string. A format string is used to describe the structure of the desired filename.
Besides using normal placeholders (such as %artist%, %title%, ...) and arbitrary text (e.g., Music) it also allows for separating folders with the backslash \ character.
Here is an example that renames the file based on the tags using the Tracknumber. Title format:
$num(%track%,2). %title%
Please note, that the $num scripting function is used to ensure double-digit track numbers.
How to create directory structures based on the tags and move the files?
When you're using a backslash in a format string, Mp3tag will create a directory from the part of the format string in front of a backslash.
Here is an example that creates new directories under D:\Music:
D:\Music\$left(%artist%,1)\%artist%-%year%-%album%\$num(%track%,2). %title%
The same is also possible using relative path names (instead of an absolute path in the example above) which creates the new directory below the current working directory:
%artist%-%year%-%album%\$num(%track%,2). %title%
Please note, that the whole range of Mp3tag's Scripting Functions can be used in the format string.