Muszę zapamiętać ten adres.

Muszę is the 1st person singular form of the verb musieć (to have to / must).

So:

• muszę = I have to / I must
• musisz = you have to
• musi = he/she/it has to

The ending -ę is a common ending for some Polish verbs in the I form, although each verb class has its own pattern.

In this sentence, Muszę already includes the subject I, so you do not need to say ja.

Polish usually does not require subject pronouns when the verb already makes the subject clear.

• Muszę already means I have to
• Ja muszę also means I have to, but ja is usually added only for emphasis, contrast, or clarification

For example:

• Muszę zapamiętać ten adres. = I have to remember/memorize this address.
• Ja muszę zapamiętać ten adres, nie ty. = I have to remember this address, not you.

So leaving out ja is the normal, natural choice here.

After muszę (I must / I have to), Polish normally uses another verb in the infinitive.

So the structure is:

• muszę + infinitive

Examples:

• Muszę iść. = I have to go.
• Muszę pracować. = I have to work.
• Muszę zapamiętać ten adres. = I have to memorize/remember this address.

This is very similar to English have to + verb.

This is a very important Polish verb distinction.

• zapamiętać = to memorize / to commit to memory / to remember from now on
• pamiętać = to remember / to have in memory

So:

• Muszę zapamiętać ten adres. means I need to get this address into my memory
• Pamiętam ten adres. means I remember this address / I know it already

In other words:

• zapamiętać focuses on the act of learning/retaining
• pamiętać focuses on the state of already remembering

This is also connected to aspect:

• zapamiętać is perfective
• pamiętać is generally treated as imperfective/state-like

Ten adres is in the accusative case, because it is the direct object of zapamiętać.

You are memorizing what?

• ten adres

For masculine inanimate nouns in Polish, the accusative singular is usually the same as the nominative singular.

So:

• nominative: ten adres
• accusative: ten adres

That is why it looks unchanged.

If the noun were a different gender or type, you might see a different form.

Because adres is a masculine singular noun, the demonstrative this must agree with it.

Polish this changes for gender:

• ten = masculine
• ta = feminine
• to = neuter

So:

• ten adres = this address
• ta książka = this book
• to okno = this window

Since adres is masculine, ten is the correct form.

Yes, adres is masculine.

A very common clue in Polish is that many masculine nouns in the dictionary form end in a consonant:

• adres
• dom
• telefon

That does not work for every noun in the language, but it is a strong general pattern.

Because adres is masculine, related words must agree with it, for example:

• ten adres
• dobry adres
• nowy adres

A rough pronunciation guide:

• Muszę ≈ MOO-sheh
• zapamiętać ≈ zah-pah-MYEN-tachch
• ten ≈ ten
• adres ≈ AH-dress

A few useful sound notes:

• sz sounds like English sh
• ć is a soft sound, roughly like a very soft ch or tch
• ę is a nasal vowel, but in normal speech its pronunciation changes depending on position
• ą in zapamiętać is also nasal, often heard roughly like on/om depending on context

You do not need to pronounce the nasal vowels exactly like French nasal vowels; in Polish they often shift depending on what follows.

The prefix za- often helps create a perfective verb, meaning the action is seen as a completed whole.

Here:

• pamiętać = to remember
• zapamiętać = to memorize / to remember successfully / to commit to memory

So the prefix helps give the idea of achieving the result: the address becomes remembered.

This is one of the many ways Polish forms aspectual pairs or related verbs, although prefixes can also add other shades of meaning in different verbs.

Usually, Muszę zapamiętać ten adres is the better choice if you mean I need to memorize this address.

Muszę pamiętać ten adres sounds less natural in that situation. It can feel like you are saying I need to keep remembering this address, but Polish often expresses that idea differently.

Common patterns are:

• Muszę zapamiętać ten adres. = I need to memorize this address.
• Muszę pamiętać o tym adresie. = I need to remember about this address / keep it in mind.

So if the idea is learn it so I don’t forget it, zapamiętać is the best fit.

Yes. Polish word order is more flexible than English, although not all orders sound equally neutral.

The most neutral version here is:

• Muszę zapamiętać ten adres.

Other orders are possible for emphasis, for example:

• Ten adres muszę zapamiętać. = This address is what I have to remember.
• Zapamiętać muszę ten adres. = possible, but more marked or stylistic

So the original sentence is the most normal everyday order.

You add nie before the conjugated verb:

• Nie muszę zapamiętać tego adresu.

This means:

• I don’t have to memorize this address.

Notice something important:

• ten adres becomes tego adresu in the negative sentence

That is because Polish often uses the genitive instead of the accusative after negation with direct objects.

So:

• affirmative: Muszę zapamiętać ten adres.
• negative: Nie muszę zapamiętać tego adresu.

The dictionary forms are:

• muszę → musieć = to have to / must
• zapamiętać → zapamiętać = to memorize / commit to memory
• ten → ten = this (masculine singular)
• adres → adres = address

This is useful because in Polish, the form you see in a sentence is often not the dictionary form, especially for verbs and nouns in different cases.

It is neutral and works in both formal and informal contexts.

There is nothing slangy or especially formal about it. You could say it in everyday speech, in writing, or in many practical situations.

For example:

• when someone tells you where they live
• when you need to remember a street address
• when you are filling out or checking contact details

So it is a very normal, standard Polish sentence.