How to interpret this NTSC color waveform?
It's an analog signal in time domain- what you would see on an oscilloscope. 

The horizontal blanking interval is when the electron beam would retrace back to the left side of the screen (but it is normally blanked so that there is no trace on the CRT screen). 

All the information is transmitted in a single analog signal with NTSC- color, luminance and sync signals. Imagine it displaying one of the upper horizontal lines in this image (Society of Motion Picture and Television Engineers SMPTE color bars from Wikipedia commons): 



There is also a vertical blanking interval and equalizing pulses to be concerned with. NTSC uses interlaced fields with 525 lines, with odd and even fields alternating at a bit under 60Hz (59.94006Hz, approximately). 

If this seems a bit complex, remember that they had to shoehorn the additional chrominance information into fixed channel bandwidths, remain backward compatible with existing monochrome television sets, and it had to be possible to get the signals out with a handful of vacuum tubes. Making the chrominance bandwidth less than the luminance bandwidth was one of the trade-offs, and was based on the response of human eye (I believe JPG compression also uses this trick). Early vacuum tube color televisions were not very stable which led to the backronym "Never Twice the Same Color" for NTSC. 

Here is an illustration of the phase relationship of the color burst reference and the displayed hue (from this site).