O carreto tem muito desgaste.

O is the masculine singular definite article, meaning the.

In Portuguese, articles are used more often than in English. So if you are talking about a specific, known carreto, Portuguese normally says o carreto, not just carreto.

Compare:

• O carreto tem muito desgaste. = The carreto has a lot of wear.
• Carreto on its own would sound more like a dictionary label, a heading, or a very context-dependent shorthand.

Because it takes o, which is the masculine singular article.

A useful pattern is that many nouns ending in -o are masculine, but the most reliable clue is the article or other words agreeing with the noun:

• o carreto
• not a carreto

So in this sentence, carreto is grammatically masculine singular.

Tem is the 3rd person singular present indicative of the verb ter (to have).

The subject is o carreto, which is singular, so Portuguese uses tem:

• eu tenho = I have
• tu tens = you have
• ele/ela tem = he/she/it has

So here, tem means has.

Because the sentence is expressing that the object has a certain amount of wear, not directly describing its state with an adjective.

• O carreto tem muito desgaste. = The carreto has a lot of wear.
• O carreto está desgastado. = The carreto is worn.

Both can be natural, but they focus on different things:

• tem muito desgaste focuses on the amount of wear
• está desgastado focuses on the condition/state

Because desgaste here is being treated as an uncountable noun, like wear in English.

So Portuguese uses singular:

• muito desgaste = a lot of wear

This is similar to:

• muita água = a lot of water
• muito tempo = a lot of time

Muitos desgastes is possible only in special contexts where you are counting different types or instances of wear, but that is much less common.

No. Here muito means much / a lot of because it comes before a noun:

• muito desgaste = a lot of wear

This is a very common point of confusion for English speakers.

Compare:

• muito desgaste = a lot of wear
• muito desgastado = very worn

So:

• muito + noun = much / many / a lot of
• muito + adjective/adverb = very

Because after a quantity word like muito, Portuguese usually uses the noun without an article.

So:

• muito desgaste = a lot of wear
• muito tempo = a lot of time
• muita areia = a lot of sand

If you added an article, the meaning would change:

• muito do desgaste = much of the wear

That refers to a specific wear already being discussed, not just wear in general.

Here muito is a quantifier/determiner agreeing with desgaste.

Because desgaste is masculine singular, the form is:

• muito desgaste

Compare the agreement:

• muito desgaste — masculine singular
• muita força — feminine singular
• muitos problemas — masculine plural
• muitas peças — feminine plural

So muito changes form depending on the noun it goes with.

Yes. That would also be natural, but it is not exactly the same.

• O carreto tem muito desgaste.
  Focus: the object has a lot of wear; slightly more technical/objective.

• O carreto está muito desgastado.
  Focus: the object is very worn; more directly descriptive.

In many real situations, either could work. The choice depends on whether you want to emphasize the amount of wear or the worn condition.

A rough European Portuguese pronunciation is:

O carreto tem muito desgaste.
≈ u kuh-REH-tu tãj MWIN-tu dzhesh-GASHT(uh)

A few important points:

• O is often reduced and sounds close to u
• tem has a nasal sound; it is not pronounced like English tem
• muito in European Portuguese often sounds close to muinto
• desgaste has a voiced zh-like sound at the start of the second syllable

If you want a more technical version, an approximate IPA transcription is:

[u kɐˈʁetu tɐ̃j ˈmũjtu dɨʒˈɡaʃt(ɨ)]

Yes. The sentence is in the present indicative.

• tem = has

So it means that, at the present time, the carreto has a lot of wear.

Depending on context, the present can also describe a current general condition, not only something happening right this second.