Она решительно закрыла ноутбук и сказала, что сегодня вечером будет отдыхать.

Because the subject is она, so the verbs are in the past tense feminine singular.

In Russian past tense, the verb changes for gender and number:

• он закрыл
• она закрыла
• оно закрыло
• они закрыли

The same pattern applies to сказать:

• он сказал
• она сказала
• они сказали

So Она решительно закрыла ноутбук и сказала... uses feminine forms because the person referred to is female.

Because ноутбук is the direct object of закрыла, so it goes in the accusative case.

For an inanimate masculine noun, the accusative singular is usually the same as the nominative singular:

• nominative: ноутбук
• accusative: ноутбук

So:

• Она закрыла ноутбук. = She closed the laptop.

If it were an animate masculine noun, the accusative would usually look like the genitive instead.

Решительно is an adverb. It describes how she closed the laptop.

It comes from the adjective решительный meaning decisive / resolute.

So:

• решительный = decisive
• решительно = decisively / firmly

In this sentence, it gives the action a strong tone: she didn’t just close the laptop; she did it in a firm, decisive way.

Because this is the compound future of an imperfective verb.

The verb отдыхать is imperfective, and imperfective verbs form the future with:

• быть in the future + infinitive

So:

• буду отдыхать
• будешь отдыхать
• будет отдыхать
• etc.

This structure often suggests a process, an activity, or a general plan:

• Сегодня вечером она будет отдыхать.
  = This evening she will be relaxing / will rest / is going to spend the evening resting.

This is a question of aspect.

Russian has two aspects:

• imperfective: ongoing, repeated, general process
• perfective: completed single result

Here:

• отдыхать = imperfective
• отдохнуть = perfective

So:

• будет отдыхать focuses on the activity itself: she will be resting/relaxing
• отдохнёт focuses more on the idea of getting some rest as a completed result

In this sentence, будет отдыхать sounds natural because it emphasizes what she plans to do that evening as an activity.

It can say что она сегодня вечером будет отдыхать, and that would be perfectly correct.

But Russian often omits a pronoun when it is clear from context. Since the main clause already has она, it is easy to understand that the same person is meant in the subordinate clause.

So both are possible:

• Она сказала, что сегодня вечером будет отдыхать.
• Она сказала, что она сегодня вечером будет отдыхать.

The version without the second она is a little smoother and less repetitive.

Here что means that and introduces a subordinate clause after сказала.

So:

• Она сказала, что... = She said that...

This is very common in Russian after verbs like:

• сказать = to say
• думать = to think
• знать = to know
• видеть = to see

In this sentence, что сегодня вечером будет отдыхать is the content of what she said.

Because Russian often expresses time with certain words in the instrumental case or with fixed adverbial expressions, and вечером is one of the common ones.

• сегодня = today
• вечером = in the evening / this evening

So сегодня вечером means this evening / today in the evening.

Other similar time expressions include:

• утром = in the morning
• днём = in the daytime / in the afternoon
• ночью = at night

You do not need a preposition here.

Because вечером is the form normally used to mean in the evening.

It is the instrumental singular of вечер:

• nominative: вечер
• instrumental: вечером

Russian often uses the instrumental case in time expressions like this:

• утром = in the morning
• днём = during the day
• вечером = in the evening

So сегодня вечером is the standard way to say this evening.

Yes, the word order can be changed, but the original order is natural and neutral.

Original:

• Она решительно закрыла ноутбук и сказала, что сегодня вечером будет отдыхать.

You could also say, for example:

• Она закрыла ноутбук решительно и сказала, что сегодня вечером будет отдыхать.
• Решительно она закрыла ноутбук и сказала, что сегодня вечером будет отдыхать.

But these alternatives shift the emphasis. The original sentence places решительно in a natural position before the verb, where it clearly modifies the action.

Russian word order is more flexible than English, but it is not random; different orders can sound more marked, literary, or emphatic.

Because the sentence describes different kinds of actions.

• закрыла: a completed action with a clear result — the laptop is now closed
• сказала: a completed act of speaking — she said it
• будет отдыхать: an ongoing or planned activity for the evening

Perfective verbs are very common for single completed events in a story. Imperfective is common when talking about a process or what someone will be occupied with.

So the aspect choices fit the meaning very well:

• first, two completed actions happened
• then she announced a future activity

Usually сказала is simply said.

The verb сказать means to say.
If Russian wants to express tell someone, it often uses:

• сказать кому-то = to tell someone / say to someone

For example:

• Она сказала мне... = She told me... / She said to me...

In your sentence, there is no person mentioned, so the basic sense is just said.

Their dictionary forms are:

• закрыла → закрыть
• сказала → сказать
• будет → быть

And for отдыхать, the form already shown is the dictionary form, because it is an infinitive.

So the sentence contains:

• закрыть = to close
• сказать = to say
• быть = to be
• отдыхать = to rest / relax

This is useful because Russian dictionaries normally list verbs in the infinitive.

It can correspond to several English translations depending on context.

• will rest
• will be resting
• is going to relax

Russian future forms do not always match one single English future form exactly.
In this sentence, будет отдыхать suggests a plan or expected activity for the evening, so in natural English you might translate it in different ways.

The important Russian idea is that it uses the future of an imperfective verb, which emphasizes the activity rather than a completed result.