PHP saving and re fetching checkbox values

I am an electronic engineering student. I have a doubt concerning Web development. I have to make a web site for doctors to enter patients data. Most of the data are in check box format. My question is regarding saving and re fetching check box status from the data base, so that the user can see what all are checked previously and what all are not checked when he log's in back the next time. And also how can i replace the check-box status in database if i change the status. I searched about this in internet but there is no much data concerning this. So if anyone could guide me or give me a link or example codes where i can look and study, it will be a great help for me.