To clarify, requirements are the qualifications which the applicant must possess in order to be eligible for a UK visa. On the other hand, supporting documents are the documentary (paper) evidence, filed with the accomplished application form, to prove that the applicant has complied with the requirement.
As an example, in applying for a UK spouse visa, one major requirement is that the applicant must be validly married to the sponsor who is a British national. Thus, In order to establish that the applicant has complied with this requirement of marriage, the supporting document which may be submitted by the applicant is the Marriage Certificate showing a valid marriage between the applicant and the British sponsor.
Please do not hesitate to call, text or email ECO-Friendly for any queries you may have pertaining to your application for a UK visa.