I'll try to word it as simply as I can to try to explain and hopefully, that will give you a better understanding. Sometimes I get a little more complex than I want to, but I'll do my best to try to keep it simple.
Contrails - can be likened to that of a car when you start it up on a cold day/morning. When you start your car in the cold and you get that white fog coming out, that's because of condensation, heat meeting the cold. Once you run the car long enough, the air temperature evens out (I don't know the science

), and the fog no longer happens.
Chemtrails - are those "clouds" that are leftover for hours (all day in some cases). They start out looking much like the above ConTrail, but unlike the contrail, these ChemTrails stay in the sky and spread out making their own sort of "cloud"-cover (which eventually, within hours, makes its way to the ground).
ConTrails = Condensation-Trails
ChemTrails = Chemical-Trails
I live by some major and minor airports and I can tell you for sure, there is a difference. I have watched the jets overhead on different days and you can see a mix of both regular air traffic as well as the ones that leave those trails. Some days around here are clear skies, and others are filled with these strips. Some of the strips have been circular, and others have been veering from left to right, and a common thing to see is criss-crossed patterns.
I believe they serve multiple purposes, what exactly, I don't know. There are those that point them to HAARP, and others to Sterilization, some even Terraforming, and others yet to numerous single projects. All I know is, it's not natural, so therefore I don't like it.
