Did you configure your IDE's linker for the library?
Considering I have no idea what that means, probably not.
Googling has taught me how to do that. I have now done that. Hurray, getting somewhere.
an include file gives the definitions of the functions and stuff so that your program passes the compile stage. But most libraries don't include the entire functions inside the .h file. The .h file just specifies function names and what data types they take as parameters. In the first compilation pass, the compiler puts in "dummy" calls to all functions that are in another module (i.e which have their body in a different .cpp file). The final "linker" stage works out the actual memory address for each function, and replaces the dummy function calls in each module with a real memory address.
Since there are different stages which are checking for different things, you need to keep and eye on what stage you get error messages. If it's during the stage when .cpp files are being processed, then it's an error in your code somewhere. If it gets to the linker stage, then it's often not a syntax error, but there was a function call where the body of the function wasn't defined in any module which has been included in the project.
Modules usually have a separate .cpp file, which also needs to be part of your project, or they have a pre-compiled .cpp file distributed as "thingname.lib" that has all the actual function bodies in it. You need to tell your IDE's linker that the lib file is part of the project otherwise you get "undefined" errors when the compiler does the final pass to stitch all the code together. In Visual C++ you can open your Properties for the project, and add your new lib to the list of libs. I think it's under a "Linker" section.