في المساء أضع الورقة والوصفة والفاتورة في الحقيبة، ثم أغلقها.

Arabic often puts a time expression at the beginning to set the scene: في المساء = in the evening.

So the sentence is framed as:

In the evening, I put ... then I close it.

This is very natural in Arabic. You could also place the time phrase later, but starting with it sounds smooth and common.

It is built into the verb.

In أضع, the prefix أـ shows first person singular, so أضع means I put / I place.

Because of that, Arabic usually does not need a separate أنا here.
You could say أنا أضع if you want emphasis, but it is not necessary.

أضع comes from the verb وضع and means I put, I place, or sometimes I am putting, depending on context.

In Modern Standard Arabic, the imperfect form can cover:

• simple present: I put
• habitual action: I usually put
• present progressive: I am putting

So Arabic does not always make the same distinction English does.

Because each noun is separately definite:

• الورقة = the paper
• الوصفة = the prescription / recipe
• الفاتورة = the bill / invoice

In Arabic, when several definite nouns are linked with و (and), it is normal to repeat ال with each one.

So Arabic prefers: الورقة والوصفة والفاتورة

rather than using ال only once for the whole list.

Because في is a very common preposition meaning in or at, and it works for both time and place here:

• في المساء = in the evening / at evening
• في الحقيبة = in the bag

So the same preposition is doing two different but related jobs:

• marking time
• marking location

They both connect things, but they are not the same.

• و means and
• ثم means then, after that

In this sentence:

• الورقة والوصفة والفاتورة uses و to join items in a list
• ثم أغلقها uses ثم to show the next action in sequence

Also, ثم usually suggests a clearer step-by-step order, sometimes with a slight pause between actions, more than و would.

ها is an attached object pronoun meaning it or her for a feminine singular noun.

So:

• أغلق = I close
• أغلقها = I close it

Here, ها refers to الحقيبة (the bag), so the meaning is:

then I close it = then I close the bag

Because الحقيبة is a feminine singular noun.

Many Arabic nouns ending in ة are feminine, and حقيبة is one of them.
So when you refer back to it with it, Arabic uses the feminine object pronoun:

• الحقيبة → ها

If the noun were masculine singular, Arabic would use ـه instead.

Grammatically, ها could refer to any feminine singular noun mentioned earlier. In this sentence, several nouns are feminine:

• الورقة
• الوصفة
• الفاتورة
• الحقيبة

But context makes الحقيبة the natural meaning, because the sentence says you put the items in the bag, and then close it. So the intended reference is clearly the bag.

It is made of:

• أغلق = I close
• ها = it (feminine singular)

Together:

أغلقها = I close it

The verb is from أغلقَ (to close / to shut), and the full first-person imperfect form is:

أُغْلِقُ = I close

With the attached pronoun:

أُغْلِقُها

A fully vocalized version would be:

فِي الْمَسَاءِ أَضَعُ الْوَرَقَةَ وَالْوَصْفَةَ وَالْفَاتُورَةَ فِي الْحَقِيبَةِ، ثُمَّ أُغْلِقُهَا.

This also shows the case endings:

• الْمَسَاءِ is genitive after في
• الْوَرَقَةَ / الْوَصْفَةَ / الْفَاتُورَةَ are accusative because they are direct objects of أضع
• الْحَقِيبَةِ is genitive after في

In normal everyday writing, these short vowels are usually omitted, but they are still understood.