N1 relates to the fan. N2 to the turbine.
Yes, that's how Cessna describe them in the Citation manuals but a more accurate description would be:
N1 is the rotational speed (usually expressed in percentage terms) of the low-pressure shaft connecting the low-pressure compressor (or fan) to the low-pressure turbine.
N2 is the similar measurement for the high-pressure shaft connecting the high-pressure compressor to the high-pressure turbine.
In the case of a three-spool engine, the N2 relates to the intermediate-pressure shaft and there will be a further reading, N3, which relates to the high-pressure shaft.
So you see that there are 'turbines' driving both (or all three) shafts. The Cessna description could imply that the 'fan' and its 'turbine' rotate at two different speeds, which is obviously not the case. (There is of course the exception of a geared fan!)
P.S. First time I've seen the definition of PACK. Thanks; makes sense!