Saya selalu beli jenama teh itu di pasar raya.

Both are possible, but they sound different in style.

• beli is very common in everyday spoken Malay.
• membeli is more formal and is more common in careful writing or formal speech.

So:

• Saya selalu beli jenama teh itu di pasar raya. = natural, conversational
• Saya selalu membeli jenama teh itu di pasar raya. = more formal

A learner will often hear bare verbs like beli in conversation.

Usually selalu means always, often, or regularly, depending on context.

In real usage, it is sometimes a little less absolute than English always. It can sound like I usually / regularly buy that brand of tea.

If you want a stronger sense of always without exception, Malay may also use sentiasa in some contexts.

In Malay, adverbs of frequency often come before the verb.

So:

• Saya selalu beli... = I always buy...
• Dia sering pergi... = He/She often goes...

Putting selalu before beli is the normal pattern.

Malay does not use articles like English a, an, and the.

Whether something is definite or indefinite is usually understood from:

• context
• word order
• words like ini and itu

In this sentence, itu helps show that a specific tea brand is meant: that brand of tea.

In Malay, demonstratives like ini and itu usually come after the noun phrase, not before it.

Examples:

• buku itu = that book
• rumah besar itu = that big house
• jenama teh itu = that tea brand / that brand of tea

So English says that brand, but Malay says brand that.

It means that tea brand or that brand of tea.

Breaking it down:

• jenama = brand
• teh = tea
• itu = that

Malay often links nouns directly like this, so jenama teh is literally tea brand.

You can say teh itu, but it means that tea, not that brand of tea.

The difference is:

• teh itu = that tea
• jenama teh itu = that tea brand / that brand of tea

So jenama is important if you want to talk specifically about the brand.

Here di means at / in and it is a preposition, so it is written as a separate word:

• di pasar raya = at the supermarket

This is different from the passive prefix di-, which is attached to a verb:

• dibeli = bought

So:

• di pasar raya = correct, separate
• dibeli = correct, attached

This is a very important spelling distinction in Malay.

Because it is a compound noun meaning supermarket.

Literally:

• pasar = market
• raya = great / major / large-scale

Together, pasar raya means supermarket. Many Malay compound nouns are written as two separate words.

Yes. Saya is the standard and polite word for I.

It is the safest choice in most situations:

• everyday polite conversation
• speaking to strangers
• writing
• formal situations

A less formal alternative is aku, but aku is more casual and can sound too direct in the wrong context.

A little, yes, but the original order is very natural.

The basic structure here is:

• Saya = subject
• selalu beli = verb phrase
• jenama teh itu = object
• di pasar raya = location

You could move the location for emphasis:

• Saya selalu beli jenama teh itu di pasar raya.
• Di pasar raya, saya selalu beli jenama teh itu.

Both are possible, but the first one is the more neutral everyday order.

It sounds natural, especially in spoken Malay.

A few style notes:

• Saya selalu beli... sounds conversational and normal.
• Saya selalu membeli... sounds more formal.
• The sentence is clear and grammatical as given.

So if you are learning everyday Malay, this is a good, usable sentence.