Después del colegio, ella merienda en casa y hace los deberes.

Because del is the required contraction of de + el.

• de el colegio → del colegio
• This contraction is used whenever de is followed by the masculine singular article el.

So:

• después del colegio = after school
• literally, after of-the school

A similar contraction is al = a + el.

It means after school or more literally after the school day / after leaving school.

In natural English, we usually say after school, not after the college/school building. Spanish often uses el colegio in this kind of everyday time expression.

So here, después del colegio is best understood as a time phrase:

• after school

This is a very common false friend.

In Spain, colegio usually means school, especially for children. It does not normally mean college in the English sense.

A few useful comparisons:

• colegio = school
• instituto = secondary school / high school
• universidad = university

So in this sentence, colegio definitely means school, not college.

Yes, you often can leave it out.

Spanish is a pro-drop language, which means subject pronouns are often omitted because the verb ending already tells you who the subject is.

So both are possible:

• Después del colegio, ella merienda en casa y hace los deberes.
• Después del colegio, merienda en casa y hace los deberes.

Both mean the same thing.

Why include ella then?

Usually for:

• emphasis
• contrast
• clarity, if you are talking about several people

For example:

• Juan juega al fútbol, pero ella merienda en casa.

So ella is not required, but it is possible and natural in the right context.

Here, merienda is a verb.

It comes from merendar, which means:

• to have an afternoon snack
• to eat a light meal in the late afternoon

In Spain, la merienda is also a noun meaning afternoon snack.

So:

• la merienda = the afternoon snack
• ella merienda = she has an afternoon snack

This is very common in Spain, where merendar is an everyday verb.

Because merienda is the conjugated form of the verb for she.

The infinitive is:

• merendar = to have an afternoon snack

The present tense forms include:

• yo meriendo
• tú meriendas
• él/ella merienda
• nosotros merendamos
• vosotros merendáis
• ellos/ellas meriendan

So ella merienda means she has an afternoon snack.

Notice the stem change:

• e → ie in most forms
  merendar → merienda

Because en casa is the usual idiomatic way to say at home.

Spanish often uses casa without an article in this expression:

• estar en casa = to be at home
• comer en casa = to eat at home
• merendar en casa = to have a snack at home

If you say en la casa, it usually sounds more like in the house/building, focusing on the physical house rather than the idea of home.

So here:

• en casa = at home

In Spanish, hacer los deberes is the normal way to say to do homework.

Spanish uses hacer for many actions where English uses do or make:

• hacer los deberes = do homework
• hacer la cama = make the bed
• hacer ejercicio = do exercise

So hace los deberes means:

• she does her homework

Even though English uses do, in Spanish the verb is simply hacer.

Because Spanish very often uses the definite article where English does not.

So although English says:

• do homework

Spanish commonly says:

• hacer los deberes

Here, los does not necessarily mean a very specific set of homework in the way the might sound in English. It is just the normal Spanish structure.

Also, in Spain, deberes is commonly used in the plural for school homework.

A related point:

• In many parts of Latin America, people often say la tarea instead.

So in Spain:

• hacer los deberes = very natural

Because in Spain, homework is commonly referred to as los deberes, a plural noun.

English uses homework as an uncountable singular idea, but Spanish often treats it differently.

So:

• los deberes = homework
• literally, something like the assignments / the tasks

This is just the normal expression in Peninsular Spanish.

You may also hear:

• hacer la tarea in many Latin American varieties

Both refer to homework, but los deberes is especially typical of Spain.

Because the present tense in Spanish is often used for habitual actions or routine.

This sentence describes what she normally does after school:

• ella merienda
• y hace los deberes

So it means something like:

• After school, she has a snack at home and does her homework.

This is the same idea as English present simple for routines:

• She eats
• She studies
• She does her homework

Because both verbs have the same subject, so Spanish normally mentions the subject only once.

Structure:

• ella merienda en casa y hace los deberes

The subject ella applies to both verbs:

• she has a snack
• and does homework

You could repeat it, but it would usually sound unnecessary:

• ella merienda en casa y ella hace los deberes

That is grammatically possible, but less natural unless you want strong emphasis or contrast.

Because Después del colegio is an introductory time phrase, and it is very common to separate that kind of phrase with a comma.

So:

• Después del colegio, ella merienda...

This helps show that the sentence starts with a time-setting expression:

• After school, ...

In short, the comma is natural and helps readability.

Yes, it sounds very natural for Spain.

Two strong clues are:

• merendar / merienda
  Very culturally typical in Spain because la merienda is a common afternoon snack.

• los deberes
  A very common Spain expression for school homework.

In other Spanish-speaking countries, people might more often say things like:

• Después de la escuela
• come algo en casa
• hace la tarea

But the original sentence is perfectly natural for Spain.

A rough guide:

• Después → des-PWES
• del colegio → del ko-LEH-hyo in Spain
• merienda → meh-RYEN-da
• deberes → deh-BEH-res

A couple of notes for Spain Spanish:

• gi in colegio sounds like a throaty h sound: ko-LEH-hyo
• ie in merienda is a diphthong, said together: RYEN

If you want a smoother rhythm, try saying the whole sentence in chunks:

• Después del colegio,
• ella merienda en casa
• y hace los deberes.