Learn Hardcore Spanish (Spain): En clase repetimos las frases siguiendo el ritmo de la música. - In class we repeat the sentences following the rhythm of the music.

You can say en la clase if you want to emphasize a specific class session or a particular classroom, but the neutral, most common way to say “in class” in Spain is en clase.

How do I know that repetimos here means “we repeat” (present) and not “we repeated” (past)?

For the verb repetir, the form repetimos is the same for:

present, nosotros → (nosotros) repetimos = we repeat
preterite, nosotros → (nosotros) repetimos = we repeated

So you need context and/or time expressions to know the tense.

In En clase repetimos las frases…, there is no past time marker (like ayer, el otro día, la semana pasada, etc.), and it’s describing what generally happens in class. That strongly suggests it’s present tense → “In class we repeat the sentences…”.

Why is there no nosotros? Why not En clase nosotros repetimos…?

Spanish usually drops subject pronouns because the verb ending already shows who the subject is.

repetimos clearly tells you it’s nosotros (we).

You only add nosotros if you want to emphasize we (as opposed to someone else) or for contrast, e.g.:

En clase nosotros repetimos las frases, pero ellos no.
In class *we repeat the sentences, but they don’t.*

In a neutral statement like your sentence, nosotros would sound a bit heavy or overly emphatic, so it’s omitted.

Why is it las frases and not just frases without any article?

Spanish uses definite articles more than English, especially when referring to a specific set of things already known in the context.

Here las frases suggests “the sentences/phrases we’re working on in this exercise / in this class,” so a specific group.

Repetimos frases (no article) would mean something more like “We repeat sentences (in general),” which sounds less natural in this classroom context.
Repetimos las frases fits the idea “we repeat the sentences (from the exercise / from the book / that the teacher gives us).”

What exactly is siguiendo doing here? How does this gerund work?

Siguiendo is the Spanish gerund of seguir (to follow). In this sentence it forms a kind of secondary action that happens at the same time and shows how we do the main action:

Main action: repetimos las frases – we repeat the sentences
Concurrent manner: siguiendo el ritmo de la música – following the rhythm of the music

So the whole idea is:
“We repeat the sentences (and we do so) while following / by following the rhythm of the music.”

Common meanings of a gerund phrase like this:

time: “while doing …”
manner / method: “by doing …”

Here it’s mainly manner and time together.

Who is doing the siguiendo? Is it we or the sentences?

Grammatically, the subject of the gerund siguiendo is the same as the subject of the main verb repetimos: nosotros (we).

So the meaning is:

We repeat the sentences, we follow the rhythm of the music.

It is not the sentences that follow the rhythm; it’s the people in class repeating them in time with the music.

Could I say En clase seguimos el ritmo de la música y repetimos las frases instead? What’s the difference?

Yes, that is grammatically correct. The difference is in style and focus:

En clase repetimos las frases siguiendo el ritmo de la música.
→ One main action (repetimos) + a simultaneous, manner-describing action (siguiendo el ritmo…). Very compact; focuses on the activity of repeating, with the music rhythm as the way we do it.
En clase seguimos el ritmo de la música y repetimos las frases.
→ Two separate actions joined by y:
1) we follow the rhythm of the music,
2) we repeat the sentences.

The original sentence sounds more like “we repeat the sentences in rhythm with the music,” not two separate steps.

Why is it el ritmo and not al ritmo here?

Because of the verb seguir, which normally takes a direct object:

seguir algo – to follow something
seguir el ritmo – to follow the rhythm

So the pattern here is seguir + direct object, which uses el, not a:

seguir el ritmo de la música – follow the rhythm of the music

You would use al ritmo de with other verbs that use a plus a complement, for example:

bailar al ritmo de la música – to dance to the rhythm of the music

But:

seguir el ritmo de la música – to follow the rhythm of the music.

Why do we say el ritmo de la música and not something like el ritmo de música?

Two points:

Article with música
Spanish usually keeps the article in structures like el ritmo de la música, because it refers to the music that is playing (a specific music in that situation), not “music” in some abstract sense.
de + el / la
- de + el → del (for masculine nouns): del libro
- de + la stays de la (for feminine nouns): de la música

So de la música is correct because música is feminine (la música).
Del música would be wrong; it would only be del with a masculine noun, e.g. del profesor.

Can I move siguiendo el ritmo de la música in the sentence? For example: En clase, siguiendo el ritmo de la música, repetimos las frases?

Yes, you can move that gerund phrase. All of these are possible and natural:

En clase repetimos las frases siguiendo el ritmo de la música.
En clase, siguiendo el ritmo de la música, repetimos las frases.
Siguiendo el ritmo de la música, en clase repetimos las frases. (more marked/emphatic)

Spanish word order is fairly flexible. Changing the position mainly affects emphasis and rhythm, not basic meaning.

The most neutral, everyday version is probably the original:
En clase repetimos las frases siguiendo el ritmo de la música.

Does en clase mean “during the lesson” or “in the classroom”? What does clase really mean here?

Clase in Spanish can refer to:

The lesson / session itself (the period of teaching), or
The group of students, or
The classroom as a place (less common; usually that’s aula in more formal language).

In En clase repetimos las frases…, the most natural reading is “when we are in (Spanish) class / during the lesson”, i.e. meaning the lesson/activity time, not the physical room.

Does frases mean “sentences” or “phrases”? I’ve also seen oraciones.

In everyday Spanish (and especially in a classroom context):

frase often means a full sentence (what English speakers call a “sentence”).
oración is the more technical/grammar term for a sentence, but many teachers and books still just say frase with learners.

So in your sentence, las frases is best understood as “the sentences” (the full sentences the teacher gives you to repeat), even though literally frase could also be “phrase” in other contexts.