What are the three steps scientists take to evaluate a scientific explanation?

A scientific explanation is a theory. Good theories make good predictions or hypothesis. Bad theories make bad predictions or hypothesis.

The theory or scientific explanation is used to make predictions or hypothesis. If the theory can not be used to make predictions it is not truly a scientific explanation.

An experiment or set of observations is designed to test the hypothesis derived from the explanation. examples would be the observations of the solar eclipse used to test Einstein's theory of relativity and the supernova studies used to test the oscillating universe theory.

The experiment or set of observations are carried out and examined and analyzed to determine if the hypothesis derived from the theory of scientific explanation actually worked.

In the case of the theory of relativity the observations verified the hypothesis and gave support for the theory which was then nearly universally accepted if not understood.

In the case of the supernova studies the hypothesis of a slowing of the rate of expansion of the universe predicted by the oscillating universe theory was disproven . The observation of three different studies all showed that the rate of the expansion of the universe was increasing. Scientists are still debating if the oscillating universe theory should be discarded and what theory should replace the oscillating universe theory.

A scientific theory or explanation must be tested using hypothesis derived from the theory. An experiment or set of observations are used to test the explanation. The results of the experiment or set of observations are used to evaluate the theory.