From the wiki at FamilySearch.org:
Having found one or more records about a person, it is time to evaluate what you found and determine how helpful and reliable it is. For example, a birth date from a birth record is probably more accurate than a birth date derived from a census record.
Evaluating the evidence takes place in several phases. It starts as soon as you find a document that must be evaluated to see if it is relevant to the family you are researching. It continues as you transfer the information from the source to your genealogical records and compose a source footnote. In that phase you are evaluating in two ways: (1) a preliminary evaluation of the reliability of the source, and (2) a comparison and contrast of data on the source with other information about the family to see if it corroborates or contradicts other sources. Later, after research on the family is mostly completed, carefully make a final, well-reasoned re-evaluation of all the sources compared to each other to help you reach a reasonable conclusion and write a proof statement subject to the Genealogical Proof Standard.
The records you have found provide evidence relative to your objective. Evidence is information or facts about an event or a situation. The researcher must evaluate if the evidence is valid for meeting the research objective and therefore producing some level of proof. You will want to consider all relevant evidence, but remember that all evidence is not equal.
The process of genealogical research seeks information (facts about events) to answer questions (research objectives) about people. The records searched are the source of the information; therefore you must evaluate both the information you found and the record(s) in which you found it.
… continues at FamilySearch.org.