I am not 100% sure, but do not think the stock Firmware will give you this level of detail. but you could install DD-WRT. and then you can use a script like for example this one

basically once on dd-wrt, you need to run this:

wget http://wrtbwmon.googlecode.com/files/wrtbwmon -O /jffs/wrtbwmon

and

chmod +x /jffs/wrtbwmon

But if you are a noob like you say, this might be a tad difficult, but nothing that can not be done with some research, and trial and error.

I am not 100% sure, but do not think the stock Firmware will give you this level of detail. but you could install DD-WRT.

[edit added below] To Install DD-WRT on this device you have to be very very carefull... there is a REAL chance of briking it! but the detailed instructions for how to install (depending on what version you have) are posted here [end edit]

and then you can use a script like for example this one

basically once on dd-wrt, you need to run this:

wget http://wrtbwmon.googlecode.com/files/wrtbwmon -O /jffs/wrtbwmon

and

chmod +x /jffs/wrtbwmon

But if you are a noob like you say, this might be a tad difficult, but nothing that can not be done with some research, and trial and error.