Measuring aggregate internet useage?

[Richard Owlett <rowlett@cloud85.net>]

I have always installed Debian from purchased DVD sets as up until about 
a year ago I was on dialup. I wish to experiment with using netinst. I 
have a minimal data cap but have accumulated enough unused capacity that 
I should be able a normal install.

I'm not sure of my search terms as the hits I get are for grossly more 
fine detail than needed. I wish to measure total usage over the time 
period of the install process.

I connect over the cell network using a T-Mobile 4G Hotspot Z915 using 
its USB connection.

Can I do what I want?
What background reading should I do?
A major motivation is self education.
TIA