N1 and N2
 

whats the difference between N1 and N2 on 737-800? thanksl

N1 relates to the fan. N2 to the turbine.

pretty much the same difference as on almost all jets i presume ?

Pritty much the same for the turboprop, NG & NP

Thanks all, last question on the 737 what are the packs exactly for?

Before you begin with airplane type specifics, you really ought to come to grips with the underlying theory.

Looking at the level of your questions, Wikipedia might help you get a general understanding of these systems. As soon as you have read up on this and have further questions, by all means do come back here.

https://en.wikipedia.org/wiki/Airbreathing_jet_engine

https://en.wikipedia.org/wiki/Pack_(aircraft)

your atpl material database really should have this, it is not difficult to understand at all

basically the system that cools the bleed air taken from the engine intakes and then released to the cabin at a reasonable temeprature

Pressurization Air Conditioning Kit = PACK

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!

To confuse the OP more, on the PW150 (Q400) we have Np, Nl & Nh, for Prop, Low pressure compressor and High pressure compressor.