Dokusan offers the opportunity to present the state of your practice to the teacher for comment and instruction. It is a chance to ask questions, discuss difficulties, and most basically, reveal who you are at that very moment. The self-consciousness, uncertainty, anxiety, and other emotional reactions that attend self-revelation are all part of what we are here to practice with.
Coming into dokusan is optional. If you do not wish an interview, when your turn comes, simply place your hands together in gassho for a few seconds, then resume your normal sitting posture.
When it's your turn for an interview and you hear the bell ring in the interview room, bow quickly from your seated position and then get up, walking with hands in shashu until your reach the open interview room door. Join the student who is waiting there with hands in gassho. Both make a full bow together on the floor. The person entering keeps their hands in gassho, the one leaving should shut the door, and return to the zendo, hands in shashu.
Walk over to the interview zabuton, (hands still in gassho) stand behind it, bow, and then kneel in seiza for the interview, sitting with your knees at the front end of the mat, nearest to the teacher. When the teacher rings the bell, ending the interview, bow from your seated position, and exit with your hands remaining in gassho.
To summarize: there are two bows entering & two bows leaving: one you do together at the door; one standing by the zabuton when entering, one kneeling on the zabuton when leaving.