El manual de instrucciones explica el reglamento.

Manual is a masculine noun in Spanish, so it takes el: el manual.

A useful tip: nouns ending in -al are very often masculine, such as:

• el hospital
• el animal
• el festival

So el manual is the normal form.

Spanish often uses the structure noun + de + noun where English might use one noun acting like an adjective.

So:

• manual de instrucciones = instruction manual

Literally, it is something like manual of instructions, but in natural English we usually say instruction manual.

This pattern is very common in Spanish:

• libro de historia = history book
• mesa de comedor = dining table
• cepillo de dientes = toothbrush

Spanish uses the definite article much more often than English. Here, el reglamento refers to a specific set of rules or regulations, so el is natural.

In Spanish, it is very common to include the article where English might sometimes leave it out. So even if English can be more flexible, Spanish often prefers:

• el reglamento
• la norma
• el documento

If the speaker has a particular regulation or rulebook in mind, el is the expected choice.

Because the subject is el manual de instrucciones, which is singular.

The main noun is manual, and de instrucciones just gives extra information about what kind of manual it is. So the subject is:

• el manual = singular

Therefore the verb must also be singular:

• explica

If the subject were plural, then the verb would be plural too:

• Los manuales de instrucciones explican el reglamento.

Because el reglamento is a thing, not a person.

In Spanish, the personal a is generally used before a specific human direct object:

• Veo a María.
• Conocemos al profesor.

But with things, you normally do not use a:

• explica el reglamento
• leo el libro
• compran la casa

So explica el reglamento is exactly what you would expect.

It can mean either, depending on context.

This is the present tense in Spanish, and the present tense is often broader than in English. It can express:

• a general fact: The manual explains the regulations
• something happening now: The manual is explaining the regulations is less natural in English, but in context Spanish present can cover a current action too

In this sentence, the most natural reading is the general statement:

• The instruction manual explains the regulations.

The infinitive is explicar, meaning to explain.

Explica is the third-person singular present form:

• yo explico
• tú explicas
• él / ella / usted explica

Since the subject is el manual, we use the él/ella/usted form:

• El manual ... explica ...

Not exactly.

• regla usually means rule
• reglamento usually means regulations, rulebook, or a formal set of rules

So el reglamento often sounds more official or institutional than la regla.

For example:

• la regla de la clase = the classroom rule
• el reglamento del club = the club regulations / rulebook

In this sentence, reglamento suggests a formal body of rules, not just one single rule.

Yes, El manual explica el reglamento is grammatically correct.

Adding de instrucciones makes the noun more specific:

• el manual = the manual
• el manual de instrucciones = the instruction manual

So de instrucciones helps clarify what kind of manual it is. Without it, the sentence is still correct, but less precise.

The normal, neutral order is:

• El manual de instrucciones
  • explica
    • el reglamento

That is subject + verb + object, which is very common in Spanish.

You can change the order in some contexts, but it usually adds emphasis or sounds less neutral. For example:

• El reglamento lo explica el manual de instrucciones.

This version puts focus on el reglamento, but it is less basic and more marked. For learners, the original word order is the best model.

You would make the nouns, articles, and verb plural as needed:

• Los manuales de instrucciones explican los reglamentos.

Changes:

• el → los
• manual → manuales
• explica → explican
• el reglamento → los reglamentos

Notice that instrucciones is already plural in the original sentence, so that part does not need to change.