Very briefly: A little... means some/ a small amount/ small in size "I'd like a little milk in my coffee" "He has a little money" "She is only a little girl." If you say "I'd like a little milk, please" you are saying - not much, but some. If you say it without the 'a' - it means not much milk at all! "I'd like very little milk, please," means that you only want a tiny bit of milk. The person pouring the milk must be careful! Only a little bit! No more! To go back to money: I have a little money... sounds good! You have some! Great! Let's go spend it! I have little money... sounds bad. Oh dear! What am I going to do? Only a few pennies/dollars/yen/ etc. One more example: He knows a little about computers. Great! I'll ask him for help. He might not be an expert but he knows something. He knows little about computers. OK, I'll ask someone else for help. He knows nothing much.

The difference is simple: A little = some. This is positive Little = not much. This is negative. 'He has a little money'. This is a positive thing. It suggests that he's able to buy what he needs. 'He has little money.' * This is a problem. It suggests that he isn't able to buy what he needs. * (or more usually 'very little' - it's rare to see 'little' used in this sense on its own in everyday English) Isn't this the same as in French? 'Un peu d'argent' as opposed to 'peu d'argent'?