दोपहर में मैं घर में आराम करती हूँ।

Because में is a postposition meaning in or at, depending on context.

• दोपहर में = in the afternoon
• घर में = in the house / at home

Hindi uses the same postposition for both time and place here. Also, unlike English prepositions, Hindi postpositions come after the noun.

Because आराम करना is a very common Hindi expression.

• आराम = rest, relaxation
• करना = to do

So आराम करना literally means to do rest, but in natural English it means to rest or to relax.

This pattern is very common in Hindi:

• काम करना = to work
• बात करना = to talk
• सफाई करना = to clean

So आराम करती हूँ is a normal way to say I rest / I relax.

Because the speaker is feminine.

In this kind of present habitual sentence, the main verb form agrees with the subject in gender and number:

• करता हूँ = used by a masculine singular speaker
• करती हूँ = used by a feminine singular speaker

So:

• If a woman says it: मैं आराम करती हूँ
• If a man says it: मैं आराम करता हूँ

हूँ is the first-person singular present form of होना (to be).

In sentences like this, Hindi often uses:

• करता/करती + हूँ

So:

• करती हूँ = I do / I am in the habit of doing

Without हूँ, the sentence would sound incomplete in standard Hindi.

This sentence is most naturally habitual or general:

• दोपहर में मैं घर में आराम करती हूँ। = I rest at home in the afternoon = I usually relax at home in the afternoon

If you want to say I am resting right now, Hindi usually uses the progressive:

• मैं घर में आराम कर रही हूँ। (feminine)
• मैं घर में आराम कर रहा हूँ। (masculine)

So करती हूँ here is not usually the same as English I am resting.

Yes, often it can be omitted if the context is clear.

Hindi frequently drops subject pronouns when the listener already knows who is being talked about.

So both can work:

• दोपहर में मैं घर में आराम करती हूँ।
• दोपहर में घर में आराम करती हूँ।

The second one is natural in conversation if it is already clear that the speaker means I.

Because Hindi normally follows Subject–Object/Complement–Verb order, and the verb usually comes near the end.

This sentence is arranged like:

• दोपहर में = time
• मैं = subject
• घर में = place
• आराम करती हूँ = verb phrase

A very typical Hindi pattern is:

time + subject + place + verb

But word order is somewhat flexible. For example, this is also natural:

• मैं दोपहर में घर में आराम करती हूँ।

Even when the order changes, the verb usually stays toward the end.

Not exactly, though they can be close in meaning.

• घर में = in the house, physically inside
• घर पर = at home, more general location

In many everyday situations, both are possible. But में often emphasizes being inside, while पर is more like at.

So:

• मैं घर में आराम करती हूँ = I relax inside the house / at home
• मैं घर पर आराम करती हूँ = I relax at home

Both can sound natural depending on context.

Because ने is not used in this type of sentence.

ने is mainly used with subjects in many perfective transitive sentences, such as:

• मैंने खाना खाया। = I ate food.

But your sentence is a present habitual sentence:

• मैं आराम करती हूँ

So ने is not needed here.

It can cover the midday/afternoon part of the day, depending on context.

In many cases:

• दोपहर = noon / afternoon
• दोपहर में = in the afternoon / at noon

For this sentence, in the afternoon is usually the most natural translation.

It is pronounced roughly like hoon, but with nasalization.

A rough pronunciation of the full sentence is:

dopahar mein main ghar mein aaraam karti hoon

A few notes:

• मैं sounds like main with nasalization
• में sounds like mein with nasalization
• हूँ sounds like hoon with nasalization

The nasal sign ँ shows that nasal quality.

करती हूँ is made of two parts:

• करती = habitual participle, feminine singular
• हूँ = first-person singular present of होना

Together they form the present habitual:

• मैं करती हूँ = I do / I usually do
• मैं आराम करती हूँ = I rest / I usually rest

So the sentence is built as:

• noun phrase for time
• subject
• noun phrase for place
• action expression आराम करना
• present habitual feminine form

That is why it sounds the way it does.