some problems about nose modelling

[kyrt]

at the both end of the second step, there are some yellow, orange and green lines at the left and right hand side of the picture.
wht is that and wht does it for?

http://www.3dluvr.com/detonum/tutorials/nosetutorial/nosetutorial.html (http://)

[Sen3D]

"The added edges are marked with red. Notice the guide splines. "

Looks like he made some splines that will have been curved to the contours of the nose in the reference image he went from so he could get an idea of what shape the model should take. Some artists do this to aid with modelling.