What is Evidence and who has the burden to present evidence?

Evidence is support for the truth of a proposition, and includes anything that makes a proposition more likely and contrary propositions less likely. Some evidence can be listed for almost anything, but a reasonable person should withhold conclusions until a high level of supporting evidence is established. The quality of evidence has to do with the credibility of the facts and the theories. Opinions and conclusions should be considered temporary, and be guided by the preponderance of evidence, and not by faith, tradition, or desire.

Any theory is accepted as provisional. It may be recognized as the best available theory until it is finally superseded by a better one, or is found false by new facts. Doubt and skepticism is how knowledge advances.

Knowledge and certainty are two different concepts and should not be confused when evaluating any issue. We can recognize that a particular theory is the best available explanation of the known data, but never achieves 100% certainty. This should not be misinterpreted as saying we know nothing, and there's nothing to choose between that and some other idea that has less or no evidence. An accepted, or established theory means that any alternative to replace it is going to have to be better, explain more, predict more, fit the facts better. Lack of 100% certainty in a theory should not be a license to believe some other idea that has even less evidence.

How can we come to the conclusion that a god does not exist? By examining the evidence that people created the god idea, and the lack of evidence that a god exist.

When a new hypothesis or theory is presented it is up to the presenter to supply the supporting evidence. At some point in the past of almost every culture, the idea of a creator god was introduced. At that time, adequate evidence for the existence of those gods was not presented, and such evidence is still absent.  It is not the responsibility of non-believers to counter these ideas by trying to prove a god does not exist. Attempting to prove something does not exist is not reasonable except for specific simple limited cases.