На работу она надела светлую блузку и удобные сандалии.

Because на работу uses the accusative case and means to work / for work.

A useful pattern is:

• на работу = to work / for work
• на работе = at work

In this sentence, на работу is understood as the destination or context: she put these clothes on for going to work / to wear to work.

So:

• Я иду на работу. = I am going to work.
• Я на работе. = I am at work.

In your sentence, it is not mainly about location; it is about what she wore for work, so на работу is the natural choice.

Russian word order is much freer than English word order. All of these are possible, depending on emphasis:

• Она надела на работу светлую блузку и удобные сандалии.
• На работу она надела светлую блузку и удобные сандалии.

Starting with на работу highlights the context first: as for work / for going to work. Then она comes next.

So the word order here sounds natural and helps organize the information, but it is not required in the same rigid way as in English.

Надела is the past tense, feminine singular form of надеть.

This tells us three things:

1. Past tense: the action happened in the past.
2. Feminine: the subject is она, so the verb takes the feminine ending -а.
3. Singular: the subject is one person.

Compare:

• он надел = he put on
• она надела = she put on
• они надели = they put on

This is a very common learner question.

• надеть = to put on something on yourself or on someone
• одеть = to dress someone

The key idea:

• надеть что? = put on an item of clothing
• одеть кого? = dress a person

So here:

• надела блузку и сандалии = she put on a blouse and sandals

Examples:

• Она надела пальто. = She put on a coat.
• Она одела ребёнка. = She dressed the child.

A traditional memory trick is:

• надеть одежду
• одеть Надежду

Not a rule by itself, but it helps remember the difference.

Because блузку is a direct object, so it is in the accusative case.

The verb надеть takes a direct object: she put on what?
Answer: блузку

Since блузка is:

• feminine
• singular
• inanimate

its accusative singular form is блузку.

The adjective must agree with the noun, so:

• nominative: светлая блузка
• accusative: светлую блузку

So both words change together.

Because сандалии is plural and inanimate, and for most inanimate plural nouns, the accusative looks the same as the nominative.

So:

• nominative: удобные сандалии
• accusative: удобные сандалии

That is why it may look like nothing changed, even though it is still the direct object.

This is very common in Russian:

• Я вижу новые дома.
• Я купила удобные сандалии.

In both cases, the inanimate plural accusative matches the nominative form.

In normal usage, сандалии is usually treated as a plural item, similar to how English often uses plural words for things worn in pairs, like glasses or pants.

So Russian commonly says:

• удобные сандалии
• новые сандалии

A singular form сандалия does exist in dictionaries, but in everyday speech the plural is much more common when talking about footwear as a pair.

So in this sentence, сандалии is exactly what you would expect.

Because they are direct objects of the verb надела.

In English, we say put on a blouse and sandals, and the object comes directly after the verb. Russian works similarly here:

• надела блузку
• надела сандалии

No extra preposition is needed.

The preposition на appears only in на работу, because that phrase expresses destination/purpose/context, not the clothing items themselves.

Because надела is perfective, and here the sentence describes a completed action: she put on those clothes.

Russian often uses the perfective past when presenting a finished event:

• Она надела светлую блузку и удобные сандалии.

If you used надевала, it would usually suggest something like:

• repeated action
• process
• background description
• habitual action in some context

For example:

• Когда было жарко, она надевала сандалии. = When it was hot, she would put on sandals.

But for a single completed act in a narrative, надела is the natural choice.

Here светлая most naturally means light-colored.

With clothing, светлый / светлая / светлую often refers to a pale or light shade:

• светлая блузка = a light-colored blouse

It can sometimes overlap with ideas like bright, depending on context, but with clothes the most natural interpretation is usually light in color, not shining or intelligent or other meanings that светлый can have in different contexts.

So in this sentence, think:

• светлая блузка = a blouse in a light color

Yes, that is grammatically possible, but it sounds a bit different in emphasis.

• На работу она надела... puts for work first, so that context is highlighted immediately.
• Она надела... на работу gives the clothing first and adds for work afterward.

Russian often moves elements around for emphasis, rhythm, and information flow. The version you were given is very natural because it frames the sentence with the occasion first: for work.