why do people demanmd money, as far as as Keynes is concerned

Three reasons

1) Transactional  - cash in pocket (no plastic in those days)
2) Precautionary  - keep a stash
3) I have forgotten - probably speculation

Why not re-read his 'General Theory' ?
- it is digestable, a fairly thin paperback also IIRC devoid of
drawings, which can be a help, but can also be a diversion.

You will score massive marks if you can distinguish between Keynes and
Sir John Hicks ... if your examiners understand either.

Look at 'Satisficing'

http://members.shaw.ca/h-chartrand/Macro%20+%203.2e.htm
The demand for money in the Keynesian Model, however, is not the same.
 Assuming income can be held either as money, spent or converted into
interest earning assets (bonds), for Keynes there were three main
reasons for holding money as cash:

i) transaction demand

ii) precautionary demand; 

iii) speculative demand; and,

iv) total demand.