Learn Hardcore Russian: Особенно полезно читать тексты, в которых есть несколько новых выражений. - It is especially useful to read texts that contain several new expressions.

особенно is an adverb meaning “especially” or “particularly.” It adds emphasis to полезно, so the phrase особенно полезно translates as “it is particularly useful.”

Why is полезно in this form, and how does it work with читать?

полезно is the neuter short-form adjective used impersonally. In Russian, adjectives like “useful” often appear in the neuter form with an infinitive verb to express general recommendations or evaluations. The pattern is:
• neuter short adjective (e.g. полезно) + infinitive (e.g. читать)
This means “it is useful to read…”

Why is читать in the infinitive, and why does it come right after полезно?

Infinitive verbs (like читать) name actions in the most general sense (“to read”). After impersonal adjectives such as полезно, Russian normally places the infinitive immediately afterward to say “it is [adjective] to [verb].” English does the same with “it is useful to read.”

Why is тексты in the accusative plural and not another case?

The infinitive читать is a transitive verb; it takes a direct object in the accusative. Since тексты is plural and you’re reading “texts,” you use the accusative plural form тексты (which, for most masculine nouns ending in a consonant, looks the same as the nominative plural).

What function does в которых serve, and can I use something else instead?

в которых is a relative pronoun + preposition meaning “in which.” It introduces the subordinate clause that describes тексты. You could colloquially say где (“where”), but в которых is more precise when referring back to an object (the texts).

Why is the verb есть used in the clause в которых есть несколько новых выражений?

Here есть means “there is/are” and sets up an existential statement within the relative clause. The structure в которых есть X literally means “in which there are X.” It’s common in Russian to use есть to say that something exists or is present.

Why does несколько require the genitive plural выражений?

In Russian, numerals or quantifiers like несколько (“several”) govern the genitive plural of the counted noun. That’s why выражения (nominative/accusative plural) becomes выражений in the genitive plural after несколько.

What does выражений mean here, and how is it different from “expressions” in English?

выражения means “expressions” in the sense of phrases, idiomatic chunks, or set phrases. English “expressions” covers both facial gestures and idiomatic phrases; in Russian, выражение лица is “facial expression,” but in linguistic contexts выражения usually means “phrases.”