Going straight to the point, what I need is some explanation about when to use fewer and when to use less. Could you also please explain to me when to use a little and little and when to use a few and few?
Less is used with uncountable nouns, like money or work or travel, and fewer is used with countable plural nouns, like coins or jobs or trips. Less is the comparative form of little and fewer is the comparative form of few. Compare the following:
* I have less work now than I had this time last year.
There are simply fewer jobs around that I am suitable for.
I therefore have little money and few friends.
Another, more common, way of saying less is not as much and another, more common, way of saying fewer is not as many. Similarly little would translate as not much and few would translate as not many. Compare the following.
* My new car doesn't use as much petrol as my old one so it's more economical.
* My new car uses less petrol than my old one so it's more economical.
* You don't see as many Peugeot 405s on the road now as you used to.
* You see fewer Peugeot 405s on the road now than you used to.
* I don't have much need to use my car in town when public transport is so good.
* I have to admit that there are few occasions when I walk anywhere nowadays.
Note that all of these uses have negative implications. If we want to be positive about something, we would use a little or a little bit of or a few. Compare the following
* I can't go out in such weather, but I have a little bit of food in the house so I shall be OK.
* I can't go out in such weather and I have little food in the house so I'm quite worried.
* A few of my colleagues turned up for my presentation, so I was quite pleased.
* Few of my colleagues turned up for my presentation, so I was quite upset.
Many / much - a lot of
Note that much and many are mostly used in negative clauses and in questions. They are not so common in affirmative clauses where we tend to use a lot of, lots of, plenty of or, very colloquially, loads of instead. Compare the following:
* In my stamp collection, I've got a lot of / lots of / plenty of Asian stamps, but I don't have very many African stamps. Do you have many African stamps in yours?
* There wasn't much traffic on the road in the snow, not very many cars and very few lorries, but, even so, there was a lot of bad driving.
* I've got loads of Simpsons videos, but not so many Simpsons comics.
Least / fewest - most
Note also that least is the superlative form of little / not much and fewest is the superlative form of few / not many. Most is the superlative form of much, many and a lot of. Compare the following:
* Jane always seems to do the least work in this office and Andy clearly does the most. I do quite a lot, but I have fewer duties than Andy. Geraldine tends to make the fewest mistakes in the work she does while Kevin makes the most.
the least - at least
Note also expressions with the least ( = the minimum) and at least ( = as a minimum requirement as well as not less than):
* You've worked such long hours today - the least I can do is to drive you back home.
* She's completed at least fifty pages of her new novel this week
* I know you're not well enough to eat anything, but at (the very) least try to drink this.