It stems from the fact that, as a rule, the definite or indefinite article in Russian, both of which do exist, are not generally used.
Russian verbs have 6 "cases", i.e.
Nominative
Accusitive
Genitive
Dative
Instrumental
Prepositional
Plus, their nouns, for example, are either male, female or neuter and they, verbs, adjectives, pronouns etc, singular and plural, must comply with whatever gender the noun is and the structure of the sentence depending on case declension etc.
Sorry if that's a wee bit confusing. Put it this way:
Example(English) Please give me a pencil (singular)
Please give me the pencils (plural)
In Russian, in this example, they would recognise the plural from the singular by simply adding a letter to the plural for pencil. Neither the definite article "the" nor the indefinite article "a" would be used at all in their sentences.
So, a strict translation of that same sentence above from the Russian would read :
Please give me pencil. (Singular)
Please give me pencils. (Plural)
(Hope this makes sense)
However, as soon as you then begin having to decline verbs etc and putting them into what are called oblique cases (N.A.G.D.I.P.), it obviously becomes more complicated but that basic rule about the definite and indefinite articles would still apply the majority of the time.
I hope you've followed that.