You should add a reference.
In the project you are working on, you can add a reference to the dll (or a library) by doing navigating to:
(Project)->References->Add Reference
[You will find Properties, References and [class]files below your project]
According to your question, you should add "UltraID3Lib.dll" to your project references and use it through adding a using
on top of your project files like this:
using HundredMilesSoftware.UltraID3Lib;
After you have successfully added the resource you should build the project and it will copy all the necessary files to your output directory (bin/Release or bin/Debug).