Relationship b/w certainity and evidence

While reading Descartes I wondered what is evidence?

In AT [18] he states when discussing his ways in which he will learn, “ the first was never to accept anything as true that I did not know evidently to be so…” Then in AT [19] he claims that only the mathematics have been able to find any demonstrations that had certain and evident reasoning.

Does Descartes mean that thoroughly self examined experience can be the equivalent to examples if said examples are certain? Even then what is certain? He puts great stress on this characteristic of knowledge but yet I cannot recall him addressing what is certain. To my knowledge mathematics do not support religion yet Descartes does. He only gives what things can be certain through his method. If I were to try and reason with one on what is certain I think it could be done with greater ease by defining (with the use of examples, like Descartes does) by what is not.