A few Newbie questions

Hi.

I have to use RRDtool for a project but am not to familar with it. I've read the tutorials I've found online but still not too sure what I'm doing

I have a couple of questions

I have a set of .rrd databases which give the Internet usage of an IP address over a timeframe. How do I extract this data to be able to say on a webpage or terminal that " 'This IP address' has downloaded X bytes this month"

Also I've seen online that you can use rrdtool with php. How would one going about doing this. I've tried the tutorial on here http://www.ioncannon.net/system-administration/59/php-rrdtool-tutorial/ but it didn't work. I would be very grateful for any help received.

Thanks in advance
Allen