A doctoral student is someone who has enrolled in a doctorate degree program. Doctoral students, sometimes called learners, may work through their studies online, on campus or both. A typical doctoral program will require students to complete a certain number of credits in coursework and successfully pass qualifying exams. This process is followed by the dissertation research, writing and defense.
A doctoral student is different from a doctoral candidate in that the student is still working through the coursework. They have not yet begun the dissertation process or passed the qualifying exams.
A doctoral candidate is someone who has completed all of the required coursework and has successfully passed their qualifying exams. Once this milestone is reached, the individual attains the unofficial status of all but dissertation (ABD).
When are you considered to be a doctor? It is only appropriate to use the title "Dr." when you are a graduate, ie, when the degree is conferred either in notice by letter or by ceremony (which ever comes first). Prior to that your status is that of a graduand. If you've been using the work-title doctoral candidate you might consider changing to Doctoral Graduand to indicate this status: that you're awaiting conferral but you've met the substantive criteria for fulfillment of your degree.