There are not defined and undefined articles (a, the) in Russian language, there are not articles at all. And what difference does it make with languages that have them?

First of all, let's define what articles A, THE in English mean:

"A/AN" is actually short version of "ONE", and "THE" is short version of "THIS".

If you want to buy a pizza in English language, you say "Give me a pizza please" or "give me this pizza please".And in Russian language one says ДАЙТЕ МНЕ ПИЦЦУ ПОЖАЛУЙСТА - give me a pizza please. And a russian seller will probably ask you: СКОЛЬКО - how many? This is what loss of articles in Russian language means - if you ask for pizza, you will be asked "how many?" because you don't say one or two etc. Sometimes when I speak English for long time, I feel lack of articles in Russian and when I switch to my native language I wanna add a/the to Russian words, Haha!