أضع البطاقة في الحقيبة حتى لا أنساها في البيت.

Because أضع already means I put / I am putting. In Arabic, the verb itself usually shows the subject, so an independent pronoun like أنا is often left out.

• أضع = I put
• أنا أضع = I put too, but with extra emphasis on I

So the sentence is perfectly normal without أنا.

أضع is in the imperfect form. In English, that can correspond to several ideas depending on context:

• I put
• I am putting
• I usually put

In this sentence, it most naturally means something like I put or I’m putting, with the idea of purpose: I do this so I won’t forget the card.

Arabic often uses a verbal sentence, where the verb comes first. So starting with أضع is very natural.

• أضع البطاقة... = literally Put-I the card...
• Natural English: I put the card...

Arabic can also use other word orders, but verb-first is extremely common.

That ending is called tāʾ marbūṭa (ة). It very often marks a feminine noun.

So:

• بطاقة = card
• حقيبة = bag

Because البطاقة is feminine, the pronoun that refers back to it later is also feminine: ها in أنساها.

A useful pronunciation note:

• In pause, ـة is usually pronounced like -a / -ah
• When grammar connects it to something after it, it can sound like t

Because the sentence is talking about specific, understood things:

• البطاقة = the card
• الحقيبة = the bag
• البيت = the house / home

Arabic often uses الـ where English may or may not use the. In particular, في البيت is a very normal way to say at home, even though English does not say in the home in this exact context.

Here حتى لا expresses purpose:

• حتى = so that / in order that
• لا = not

So together, حتى لا أنساها means:

• so that I do not forget it
• in order not to forget it

A very natural English equivalent is so I don’t forget it.

This is a very common question.

After حتى, Arabic often has an understood or implicit أن, so you do not normally add a separate written أن here.

So:

• حتى لا أنساها = correct
• حتى لا أن أنساها = wrong

Also, do not confuse the beginning of أنساها with the separate particle أن. In أنساها, the word is just the verb أنسى (I forget) plus ها (it).

A more advanced note: after حتى, the verb is understood as being in the subjunctive, but with this particular verb the spelling looks the same.

أنساها breaks down like this:

• أنسى = I forget
• ها = it / her

So أنساها means I forget it.

In this sentence:

• حتى لا أنساها = so that I do not forget it

The ها refers to البطاقة.

Because البطاقة is a feminine singular noun, and Arabic object pronouns must match that.

So:

• ها = it / her for a feminine singular noun
• أنساها = I forget it

If the noun were masculine, you would use a different pronoun.

Grammatically, both البطاقة and الحقيبة are feminine singular, so ها could in theory point to either one.

But in actual meaning, the sentence clearly intends البطاقة:

• I put the card in the bag so that I don’t forget it at home

Context is what tells you which noun is meant. This is normal in Arabic, just as pronouns in English sometimes depend on context too.

Because Arabic commonly says في البيت, literally in the house, where English often says at home.

So:

• في البيت = at home / in the house

This is simply the normal Arabic expression. It does not sound strange to Arabic speakers.

Because في is the normal preposition for putting something in or inside something.

So:

• أضع البطاقة في الحقيبة = I put the card in the bag

Using إلى here would not sound natural, because إلى means to / toward, not inside in this kind of sentence.

You could also say داخل الحقيبة for extra emphasis on inside the bag, but في الحقيبة is the most straightforward and natural choice.

A fully vocalized version is:

أَضَعُ البِطاقَةَ فِي الحَقِيبَةِ حَتّى لا أَنْساها فِي البَيْتِ.

This shows the grammar more clearly:

• أَضَعُ = verb, I put
• البِطاقَةَ = direct object, so it takes fatḥa
• فِي الحَقِيبَةِ = after في, so kasra
• فِي البَيْتِ = also after في, so kasra

In normal everyday Arabic writing, these short vowels are usually omitted.