As a matter of fact, here's the classic ye olde The Pits tutorial from about, what.... 15 years ago?
http://www.thepits.us/files/tutorials/SandboxTrackTutor.pdf
Keep in mind that while many of the methods to create tracks have been expanded upon (and even updated to the point where just about everything in the PDF is outdated), it's still better to have that as a starting point and is something you should read irregardless if it's not "up-to-date" on modern NR2003 track creation.
*EDIT* Oh, and depending on what OS your computer has, Sandbox may give you issues (especially on Windows 8 and later) due to it's occasional instability, so do be cautious when using the program as well.