Para dibujo técnico, la profesora dijo que trajéramos un compás y una regla larga.

With school subjects, Spanish often leaves out the article, especially after prepositions like para, en, or de.

So para dibujo técnico means for technical drawing or for technical drawing class.

If you want to be more explicit, you could say para la clase de dibujo técnico, but the shorter version is very natural.

Yes. Profesor is masculine and profesora is feminine.

So:

• el profesor = the male teacher
• la profesora = the female teacher

In this sentence, la profesora tells you the teacher is a woman.

Dijo que is the normal way to report what someone said: she said that...

But here it is not just a neutral statement. The teacher was giving an instruction, so Spanish uses dijo que + subjunctive to report that instruction:

• La profesora dijo que trajéramos... = The teacher said that we should bring...

This is a very common pattern when reporting orders, requests, or instructions.

Because the teacher’s words are being reported as a command or instruction, not just as a fact.

Compare:

• Dijo que venía = She said she was coming.
  This reports information.
• Dijo que viniéramos = She said that we should come.
  This reports an instruction.

So in your sentence, trajéramos is used because the meaning is basically she told us to bring those items.

Trajéramos is the nosotros form: that we bring / that we should bring.

That means the speaker is including themselves in the group of students.

• trajéramos = we should bring
• trajerais = you all should bring (vosotros, used in Spain)

So the sentence is being told from the students’ point of view: the teacher said that we should bring...

If the speaker were reporting it to someone else and addressing classmates as you all, then trajerais could be used instead.

It comes from the verb traer.

The imperfect subjunctive is built from the preterite stem. For traer, the preterite third person plural is trajeron. From that, you get the stem traj-, and then the imperfect subjunctive endings are added:

• trajera
• trajeras
• trajera
• trajéramos
• trajerais
• trajeran

The accent in trajéramos is normal in the nosotros form of the -ra imperfect subjunctive series. It shows where the stress falls.

Yes. Spanish has two correct imperfect subjunctive forms:

• trajéramos
• trajésemos

Both are grammatical and mean the same thing here.

In everyday speech, -ra forms such as trajéramos are usually more common. The -se forms can sound a bit more formal or literary, though they are still completely normal.

Compás is a masculine noun, so it takes un:

• un compás

Even though the word ends in -ás, it is still masculine. Gender in Spanish does not always depend on the final letter alone, so it is something you often just have to learn with the noun.

Because Spanish normally gives each separate countable item its own article.

So:

• un compás
• una regla

This is especially natural here because the two nouns have different genders: compás is masculine and regla is feminine.

In Spanish, adjectives usually come after the noun.

So:

• regla larga = long ruler

It is larga because it agrees with regla, which is feminine singular:

• regla = feminine singular
• larga = feminine singular

If the noun were masculine, you would use largo.

It describes only regla.

So the phrase means:

• a compass
• and a long ruler

It does not mean that both items are long.

If you wanted the adjective to apply to both nouns, Spanish would normally phrase it differently, for example with a plural adjective agreeing with the whole group.

The basic difference is:

• traer = to bring, toward the speaker or destination being focused on
• llevar = to take, carry away from the speaker’s point of view

Here, the idea is bring these things to class, so traer fits well.

That said, in real life, Spanish speakers sometimes use llevar too, depending on the perspective:

• Traed un compás a clase
• Llevad un compás a clase

Both can be natural, but traer works very well when the destination is the classroom/teacher context.

Because Spanish often leaves out subject pronouns when the verb ending already makes the subject clear.

Trajéramos already tells you the subject is nosotros.

So Spanish normally says:

• dijo que trajéramos

not

• dijo que nosotros trajéramos

You can add nosotros for emphasis or contrast, but it is not necessary.

The comma separates the introductory phrase Para dibujo técnico from the main part of the sentence.

It gives the sentence a slight as for technical drawing... feeling:

• Para dibujo técnico, la profesora dijo...

This kind of comma is common when a phrase is placed at the front to set the context. In some similar sentences, especially shorter ones, you may also see no comma, depending on style.