V té učebnici jsou krátké texty a já se z ní učím každý večer.

Because the preposition v meaning in requires the locative case here.

• Basic dictionary form: ta učebnice = that textbook
• After v: v té učebnici = in that textbook

Both words change because they must agree in case, gender, and number:

• ta → té
• učebnice → učebnici

So v té učebnici literally means in that textbook.

It is in the locative singular.

The noun učebnice is a feminine noun. Its forms here are:

• nominative: učebnice
• locative singular: učebnici

Since it comes after v in the meaning in, Czech uses the locative:

• v učebnici = in the textbook
• v té učebnici = in that textbook

Jsou is the 3rd person plural form of být (to be), and it agrees with krátké texty (short texts), which is plural.

So:

• jsou krátké texty = there are short texts / short texts are

In Czech, this is a normal way to say that something exists somewhere:

• V té učebnici jsou krátké texty. = There are short texts in that textbook.

English often uses there are, but Czech simply uses jsou.

Because the adjective must agree with the noun.

Here, texty is:

• masculine inanimate
• plural
• nominative

So the adjective krátký changes to krátké:

• singular: krátký text = a short text
• plural: krátké texty = short texts

This is basic adjective-noun agreement in Czech.

Because the verb for to study / to learn in this sense is učit se.

Compare:

• učit = to teach
• učit se = to learn / to study

So:

• Učím češtinu. = I teach Czech.
• Učím se češtinu. = I am learning Czech.

In your sentence:

• já se z ní učím = I study from it / I learn from it

The se is not optional here; it is part of the verb’s meaning.

Because z (from/out of) requires the genitive case, and the pronoun referring to učebnice must match that.

Učebnice is feminine, so the pronoun is based on ona (she/it for feminine nouns). After a preposition, Czech uses forms like ní instead of jí in this structure.

So:

• z učebnice = from the textbook
• z ní = from it

In natural English, učím se z ní means I study from it.

Yes, literally it is something like I learn/study from it.

Czech often uses učit se z + genitive to express studying from a source, especially a book or textbook:

• učím se z knihy = I study from a book
• učím se z učebnice = I study from a textbook
• učím se z ní = I study from it

English often prefers study from it or just use it to study, but Czech naturally uses z here.

Because Czech often uses the accusative of time for repeated time expressions.

So:

• každý večer = every evening
• každý den = every day
• každý týden = every week

No preposition is needed.

Also note the adjective agreement:

• večer is masculine singular
• so každý is the correct form

Yes, it can be omitted.

Czech often drops subject pronouns because the verb ending already shows the person:

• učím se = I study / I am learning

So the sentence could also be:

• V té učebnici jsou krátké texty a z ní se učím každý večer.

The pronoun já is included for:

• emphasis
• contrast
• clarity

It can sound a bit more explicit, like and I study from it every evening.

Yes, Czech word order is flexible.

The given order is natural, but other versions are possible:

• A já se z ní učím každý večer.
• A každý večer se z ní učím.
• A z ní se učím každý večer.

The meaning stays basically the same, but the focus changes slightly:

• každý večer at the end can sound neutral and natural
• putting z ní earlier can emphasize from it
• putting každý večer earlier can emphasize the time

Czech word order often depends on what is new, important, or emphasized.

Yes, učebnice is feminine.

A good clue is the ending -e, and more importantly, the way it behaves in declension:

• nominative: ta učebnice
• locative: v té učebnici
• genitive with noun: z učebnice
• pronoun reference: z ní

You can also see its gender from agreement:

• ta učebnice uses the feminine demonstrative ta
• later it is referred to by feminine ní

So the sentence gives you several clues that učebnice is feminine.

It means texts in a broad sense, and in a textbook context it often means reading passages or short written pieces.

So krátké texty could mean:

• short texts
• short passages
• short reading passages

The exact English translation depends on context, but grammatically it is simply the plural of text:

• text = text
• texty = texts