Learning more about fitting non-linear lines...

Many of the graphs used in biochemistry are non-linear curves. These include the calculation of LD50 and IC50 as well as the majority of curves associated with enzyme kinetics.

For these reasons, I am trying to understand more about the nls() function in R.

A Google search has revealed the following links which I am reading through:

• https://stat.ethz.ch/R-manual/R-patched/library/stats/html/nls.html
• key documentation supplied with R. 
• http://robinlovelace.net/2013/10/23/nls-demonstation.html
• contains info about how to calculate a r^2 value. 
• http://www.walkingrandomly.com/?p=5254
• Shows an example of an irregular set of points and a nicely fitted line.
• https://rmazing.wordpress.com/2012/07/05/a-better-nls/#comments
• I found this through r-bloggers.com - there is a lot at the rmazing site about non linear modelling

Hmm, this is all quite technical and maybe even a bit more complicated than I need but hey....