To Import the Model into your Scene, choose "File - Append", then choose the file you've downloaded, then go to Groups and insert either the Group "Grand Piano", "Bench" or both according to your needs. 

All Interiors are also grouped as the named Group "Interiors", so that you easily can pick all interior parts and separate them for the sake of render Scene size in case the Piano is closed.  

You will also find a Group "zzz_Studio_Lighting", which is a preinstalled Studio Setup, so that just need to hit render and get an instant result. The Studio Setup is a free giveaway which you can use for any purposes.

Note on rig usage

To control certain parts of the Piano, use the arrows of the Control Panel wich is available in the 3D Viewport. Rotate the arrows along their local X-axes by pressing r-x-x. Please note that the Control for the Part "Top Board Front" has a rotation Limit of 179,9° instead of 180°, because Blender can not handle 180° Turns (Flipping Error is a known Blender issue). 

 Credit For Music Notes Image Texture The Image Texture of the Music Notes is taken from http://imslp.org/wiki/Piano_Sonata_No.16_in_C_major,_K.545_%28Mozart,_Wolfgang_Amadeus%29 and released under Creative Commons Attribution-ShareAlike 4.0 License