Boeshield T-9 Lubricant ?

Hi,

Son and daughter in law now have brand new bikes.

Would like to get them to learn a bit about the necessity and
desirability of lubricating the chains.

a. Is Boeshield T-9 what I want to get them ?
Or,...?

b. How does one use it ? How often ?

Necessary to get rid of old lubricant first,
or O.K. to just add a few drops to a rag and go over the chain with
it (and not worry about what is on it already) ?

c. Also use on the gear Sprockets ?

Thanks,
Bob