Not only are the elements that make up how a particular type of source should be cited dictated by rules and convention, so are the form, order and punctuation used, according to the citation (i.e. bibliographical) style in question. It is therefore not up to you which elements you set in boldface or underline, or whether you state the first name or only the initials of an author. Reference style books dictate how this is done.
A reference style is often specific to a certain academic discipline or academic journal. Among the styles often encountered are APA, Harvard, Chicago and MLA. If necessary, find out from your degree programme department whether a specific style is required when writing papers or theses.
Applying a certain style allows you to cite sources correctly and consistently.