As instruções causaram confusão.

Because instruções is a feminine plural noun, so it takes the feminine plural definite article as.

• a instrução = the instruction
• as instruções = the instructions

Portuguese articles must agree with the noun in gender and number.

Many Portuguese nouns ending in -ão form the plural as -ões.

So:

• instrução → instruções

This is a very common plural pattern, though not the only one. Other nouns in -ão may form plurals in -ães or -ãos, so this is something learners usually need to memorise word by word.

Because the subject is plural: as instruções.

Portuguese verbs change form to match the subject:

• A instrução causou confusão. = The instruction caused confusion.
• As instruções causaram confusão. = The instructions caused confusion.

So causaram is the 3rd person plural form, while causou is 3rd person singular.

Causaram is the pretérito perfeito (simple past / preterite) of causar.

Here it refers to a completed action in the past: the instructions caused confusion.

Basic forms:

• eu causei
• tu causaste
• ele/ela causou
• nós causámos (in European Portuguese spelling)
• eles/elas causaram

This tense is often used for a finished event.

The difference is mainly about how the action is viewed.

• causaram = they caused, as a completed event
• causavam = they were causing / used to cause, more ongoing, repeated, or backgrounded

So:

• As instruções causaram confusão.
  This sounds like a specific completed result.

• As instruções causavam confusão.
  This would suggest they were repeatedly or generally causing confusion.

Portuguese often uses abstract nouns without an article when speaking in a general sense.

So causaram confusão means caused confusion in a broad, natural way.

You could also say:

• causaram uma confusão

but that usually sounds more like caused a confusion / caused a mess / created a scene, often more concrete or more dramatic.

So in this sentence, no article is very natural.

Because causar normally takes a direct object.

Structure:

• causar + something

So:

• causar confusão
• causar problemas
• causar dano

Unlike some English verbs that may need a different structure, here Portuguese simply puts the noun directly after the verb.

Yes, but the original order is the most neutral and natural:

• As instruções causaram confusão.

You could also use a passive structure:

• A confusão foi causada pelas instruções.

This is grammatically correct, but it is less direct and puts the focus on confusão rather than on as instruções.

So the original sentence is usually the best choice in ordinary speech and writing.

A rough European Portuguese pronunciation guide would be:

az in-stru-SOYN-sh kaw-ZA-rãw kõ-fu-ZÃW

A few helpful points:

• As sounds more like az here because it comes before a vowel in instruções.
• -ções has a nasal sound and ends roughly like -sh.
• -am at the end of causaram is nasal; it does not sound like English am.
• confusão also ends in a nasal sound.

You do not need to pronounce every written vowel strongly; in European Portuguese, many unstressed vowels are reduced.

Yes, causar is common and perfectly natural. It is slightly formal-neutral and works very well in writing.

Some alternatives are:

• provocar confusão = to provoke/cause confusion
• gerar confusão = to generate confusion
• criar confusão = to create confusion

All are possible, but causar confusão is straightforward and standard.