בפסקה הראשונה המורה מדגישה שתי מילים חדשות.

In Hebrew, short prepositions often attach directly to the following word.

Here, ב־ means in or at, so:

• פסקה = paragraph
• בפסקה = in a paragraph / in the paragraph

So unlike English, Hebrew does not need a separate word for in here.

Because the phrase is definite.

What is happening is:

• הפסקה = the paragraph
• after the preposition ב־, the ה־ of the definite article is absorbed
• so ב + הפסקה becomes בפסקה

In unpointed Hebrew, you do not see the vowel change, but the structure is still definite.

Also, הראשונה has the definite article ה־, which confirms the whole phrase is definite:

• פסקה ראשונה = a first paragraph
• הפסקה הראשונה = the first paragraph
• בפסקה הראשונה = in the first paragraph

Because in Hebrew, adjectives usually come after the noun they describe.

So:

• פסקה ראשונה = first paragraph
• literally: paragraph first

This is normal Hebrew word order for adjectives.

Also, the adjective must agree with the noun in:

• gender
• number
• definiteness

So ראשונה is feminine singular because פסקה is feminine singular.

הראשונה is an ordinal number used like an adjective, meaning first.

It is the feminine singular form of ראשון / ראשונה:

• masculine singular: ראשון
• feminine singular: ראשונה

Since פסקה is feminine, Hebrew uses ראשונה.
Since the phrase is definite, it becomes הראשונה.

Because Hebrew verbs in the present tense agree with the subject in gender and number.

מדגישה is:

• present tense
• singular
• feminine

So it means she emphasizes or is emphasizing.

If the teacher were male, it would be:

• המורה מדגיש = the teacher emphasizes

By itself, המורה can mean either the male teacher or the female teacher.

The noun מורה is one of those Hebrew words whose form can be used for both genders.
You find out the gender from other words in the sentence, especially the verb.

Here, the verb is מדגישה, which is feminine, so the sentence refers to a female teacher.

It is the present tense.

In modern Hebrew, the present tense form can often correspond to either:

• emphasizes
• is emphasizing

The exact English choice depends on context. Hebrew does not usually make that distinction as sharply as English does.

So המורה מדגישה can mean either:

• the teacher emphasizes
• the teacher is emphasizing

Because מילה is a feminine noun, and the number two must match that gender.

Before a noun:

• שני is used with masculine nouns
• שתי is used with feminine nouns

So:

• שני ספרים = two books
• שתי מילים = two words

Since the singular is מילה and that noun is feminine, Hebrew uses שתי.

Because Hebrew noun gender is not always predictable from the plural ending.

The singular noun is:

• מילה = word

This noun is feminine. Its plural is:

• מילים

Even though ־ים often marks masculine plural, some feminine nouns have irregular or less predictable plural forms.
So you have to learn the noun’s gender as part of the word.

A clue here is the adjective:

• חדשות

That is a feminine plural adjective, so it shows that מילים is being treated as feminine plural.

חדשות is an adjective meaning new, and Hebrew adjectives normally come after the noun.

So:

• מילים חדשות = new words

Its form is feminine plural because it agrees with מילים:

• חדשה = new, feminine singular
• חדשות = new, feminine plural

Since מילים is feminine plural, the adjective must also be feminine plural.

Notice that there is no ה־ on חדשות, because שתי מילים חדשות is not definite. It means two new words, not the two new words.

Yes. Hebrew word order is somewhat flexible.

This sentence begins with בפסקה הראשונה to set the scene first:

• בפסקה הראשונה המורה מדגישה שתי מילים חדשות.

That is very natural and means something like:

• In the first paragraph, the teacher emphasizes two new words.

Hebrew could also say:

• המורה מדגישה שתי מילים חדשות בפסקה הראשונה.

That is also grammatical. The difference is mostly about emphasis and flow, not basic meaning.