La professora explica que el passaport i el mapa són importants per al viatge.

Because professora is a feminine singular noun, so it takes the feminine singular article la.

• la professora = the (female) teacher
• The masculine form would be el professor = the (male) teacher

In Catalan, articles must agree with the noun in gender and number.

Because not all Catalan nouns ending in -a are feminine. Mapa is a masculine noun, so it takes el:

• el mapa = the map

This is a common pattern with some words of Greek origin, such as:

• el problema
• el sistema
• el tema

So you cannot assume that every noun ending in -a is feminine.

Catalan normally includes the article with each noun:

• el passaport i el mapa

This is more natural in Catalan than using one article for both nouns. In English, the passport and map sounds fine, but Catalan often prefers repeating the article when referring to two separate specific things.

Here que means that and introduces a subordinate clause:

• La professora explica que...
• The teacher explains that...

It connects the main verb explica with the idea being explained.

Because the subject is plural:

• el passaport i el mapa = the passport and the map

Two things joined by i (and) make a plural subject, so the verb must also be plural:

• és = is
• són = are

So:

• el passaport és important = the passport is important
• el passaport i el mapa són importants = the passport and the map are important

Because importants is a plural adjective, and it agrees with the plural subject:

• important = singular
• importants = plural

Since el passaport i el mapa refers to two things, Catalan uses the plural form:

• són importants = are important

Because per al here means for the.

It comes from:

• per a = for
• el = the

Together:

• per a + el → per al

So:

• per al viatge = for the trip

This is a very useful pattern to recognize. In less formal language, you may also hear pel viatge in some contexts and varieties, but per al viatge is a standard way to say for the trip.

Usually Catalan keeps que after verbs like explicar, dir, pensar, and creure when introducing a full clause.

So this is the normal structure:

• La professora explica que el passaport i el mapa són importants...

In English, we often say:

• The teacher explains the passport and map are important...

without that. In Catalan, keeping que is much more natural, especially in standard written language.

Són is the 3rd person plural form of ser (to be).

Here are a few forms of ser in the present tense:

• és = is
• són = are

So in this sentence:

• el passaport i el mapa són importants
• the passport and the map are important

The accent mark in són is part of the normal spelling.

Yes. Catalan often has masculine and feminine forms for professions:

• professor = male teacher
• professora = female teacher

This is very common:

• alumne / alumna
• director / directora
• metge / metgessa

So la professora clearly tells you the teacher is female.