What was Nixon's plan to "win" the Vietnam War? How did this plan involve Cambodia?

President Nixon had a three parts to his plan to end the
war.

First, he wanted the North Vietnamese to withdraw
their military from the South.

Second, he wanted to end the
kind of domestic unrest that was causing the protests against the war at home.  He did
this by making the draft fairer and eventually ending
it.

Third, he wanted to fight the war more aggressively. 
This included bombing Cambodia because there were places in that country where communist
troops would set up bases in safety (because the US would not attack them in a neutral
country.)