If you go to your user folder, you can right click on the properties of your folders (i.e. Documents, Music, Photos, Videos, Downloads, etc...) and choose "location". Assuming your C: is the SSD, and the D: is the WD Black, change the location from C:\USERS\USERNAME\DOCUMENTS to D:\USERS\USERNAME\DOCUMENTS - it will ask you if you want to move the files, say yes - and that is moved.
If you are installing programs that you want on the WD Black, again, choose custom install, and change the "C:" to a "D:", and it will be installed to the hard drive.