1.      Why do we have to put the in-text citation reference after the text and then again on the reference page

2.      How will I know I have gotten the citation from a credible source or is there a tool that would be able to tell,

3.      can I use a part of a sentence, and When is citing considered to be too long? I read many articles on the Internet but was so unsure as to which of them was credible enough to get my citing.