Why is the indefinite article used with uncount nouns in these examples?
1)Let's have a coffee! or Would like a coffee?
2)a job & some work
3)Can I have a Coke?
As I know, we can put countable expressions in front of the nouns to make them countable.F.e.,a cup of coffee, a can of Coke.Or it isn't important to use such kind of expressions & we can omit them? So,why is the indefinite article used with uncount nouns in these examples?
What's the difference between "job and work" and the reason of putting the indefinite article? They have the same meaning, don't they?

Question

Answer

Yes, we can use "a coffee" to mean "a cup of coffee", for example. However, if you are speaking in general you would say "I like coffee" or "I'm addicted to coffee". Same with "a Coke" - there's an implied unit, from the context (ie. Coke is served in cans).

"Job" is countable ("task" is also countable, by the way) but "work" is uncountable, unless you mean "an artistic creation" such as "a work by Beethoven".

By the way, we use "eg." to mean "for example". It's a Latin term, and we would read it as either "E G" or "for example".  "F.e" and "ex." are not really natural.

Answer

A coffee means a cup of coffee, a coke means a can of coke or whatever it is served in. Job and work have similar meanings but work is uncountable when used in this sense. Look on the bright side -- we have no grammatical cases.