Cuando hace buen tiempo, mi madre lee en la terraza con un cojín en la silla mientras yo estudio dentro de casa.

In Spanish, weather expressions often use hacer:

• Hace frío = It’s cold
• Hace calor = It’s hot
• Hace sol = It’s sunny
• Hace buen tiempo = The weather is nice / It’s good weather

So here hacer does not literally mean to make. It is just the normal verb used in many weather expressions.

Bueno becomes buen before a singular masculine noun.

• un buen libro
• buen tiempo

Since tiempo is a singular masculine noun, Spanish uses buen here.

This shortening happens only before the noun:

• el tiempo es bueno
• hace buen tiempo

In this sentence, tiempo means weather, not time.

Spanish tiempo can mean both:

• time
• weather

You understand the meaning from context. In hace buen tiempo, it clearly means the weather is good.

Because this is a fixed weather expression. Spanish normally says:

• hace buen tiempo
• hace mal tiempo

You do not usually say hace un buen tiempo in this basic weather sense. It is treated as a general expression, much like it’s nice weather.

In modern Spanish, possessives normally go directly before the noun without an article:

• mi madre
• tu casa
• su libro

So mi madre simply means my mother.

Using an article plus possessive is not the normal modern pattern here.

The sentence describes a habitual or typical situation:

Cuando hace buen tiempo, mi madre lee... mientras yo estudio...

This means something like:

• Whenever the weather is nice, my mother reads... while I study...
• When the weather is nice, my mother reads... while I study...

Spanish often uses the present tense for regular actions or general truths, just like English can.

Cuando means when. Here it introduces the condition or circumstance under which the rest happens.

So the structure is:

• Cuando hace buen tiempo = When the weather is nice
• mi madre lee... = my mother reads...
• mientras yo estudio... = while I study...

Putting the cuando clause first is very natural, and that is why there is a comma after it.

Sometimes yes, but the meaning changes slightly.

• Cuando hace buen tiempo = when(ever) the weather is nice
  This sounds like a usual or repeated situation.
• Si hace buen tiempo = if the weather is nice
  This sounds more conditional or uncertain.

In your sentence, cuando fits well because it describes a typical routine.

Because the sentence begins with a subordinate clause. In Spanish, when a clause like cuando..., si..., or aunque... comes first, it is very common to put a comma before the main clause.

So:

• Cuando hace buen tiempo, mi madre lee...

If the order were reversed, the comma would often disappear:

• Mi madre lee en la terraza cuando hace buen tiempo.

En is the normal preposition for location here: on / in / at the terrace, depending on how English would express it.

So:

• en la terraza = on the terrace / out on the patio / on the balcony-area, depending on context

Spanish uses en much more broadly than English uses in.

It means with a cushion on the chair.

The most natural interpretation is that the cushion is on the chair, and the mother is reading there comfortably.

So the phrase is understood as:

• my mother reads on the terrace, with a cushion on the chair

It does not normally mean she is somehow carrying the cushion herself. The phrase en la silla helps show where the cushion is.

Cojín is the normal word for a cushion in Spanish.

In Spain, cojín is very common for a cushion used on a chair or sofa. Depending on context, other words can exist, but cojín is the basic, straightforward choice here.

Mientras means while. It shows that two actions happen at the same time:

• mi madre lee
• yo estudio

So:

• mientras yo estudio = while I study

It connects simultaneous actions very naturally.

Spanish often omits subject pronouns because the verb ending already shows the subject:

• estudio already means I study

But yo can be included for clarity or contrast. Here it helps create a nice contrast:

• mi madre lee...
• mientras yo estudio...

So yo is not required, but it is perfectly natural because it emphasizes I, as opposed to my mother.

Without it, the sentence would still be correct:

• ...mientras estudio dentro de casa

Both are possible, but they are not exactly the same.

• estudio = I study / I am studying
• estoy estudiando = I am studying right now

In Spanish, the simple present often covers what English expresses with either the present simple or present continuous, especially in general or habitual contexts.

Since the whole sentence describes a usual situation, estudio sounds very natural.

Both can mean something like at home or inside the house, but dentro de casa is more explicit about being inside.

• en casa = at home
• dentro de casa = inside the house

Here the sentence contrasts two places:

• en la terraza = outside/on the terrace
• dentro de casa = inside the house

So dentro de casa is chosen to make that contrast clearer.

Both can exist, but dentro de casa is very common when speaking generally about being inside the home.

It sounds a bit more natural and idiomatic in many everyday contexts. Adding la can sound more specific, as if you are referring to a particular building as an object.

So here:

• dentro de casa = inside the house / indoors

is the most natural phrasing.

The word order is natural, but Spanish is somewhat flexible.

The sentence is organized like this:

1. Cuando hace buen tiempo — sets the scene
2. mi madre lee en la terraza — main action
3. con un cojín en la silla — extra detail
4. mientras yo estudio dentro de casa — simultaneous action

You could move some parts around, but the original order sounds smooth and easy to follow.

For example:

• Cuando hace buen tiempo, mi madre lee con un cojín en la silla en la terraza mientras yo estudio dentro de casa.

This is possible, but a bit less elegant than the original.

No. Lee has no written accent.

It comes from the verb leer:

• yo leo
• tú lees
• él/ella lee

Even though two vowels come together, there is no accent mark in lee.

A close, natural English version would be:

When the weather is nice, my mother reads on the terrace with a cushion on the chair while I study inside the house.

Or a slightly more natural English version:

When the weather is nice, my mother sits reading on the terrace with a cushion on her chair while I study indoors.

The Spanish itself is completely natural; English just sometimes prefers slightly different phrasing for comfort and style.