A minhoca apareceu junto ao rebento enquanto eu usava o regador.

Because a minhoca means the worm. Portuguese very often uses the definite article where English might or might not, especially when talking about a specific thing in the scene.

So here:

• a minhoca = the worm
• minhoca on its own = worm in a more general or dictionary-style sense

Apareceu is the pretérito perfeito simples of aparecer for ele/ela/você. It is used for a completed event in the past.

Here, the worm’s appearance is treated as a single event:

• A minhoca apareceu... = the worm appeared / showed up

If you used aparecia, it would sound more like a repeated, ongoing, or descriptive action:

• A minhoca aparecia... = the worm used to appear / was appearing

Because usava is the imperfect, and it fits the idea of a background action that was already in progress when something else happened.

In this sentence:

• apareceu = the main event that happened
• usava = the ongoing background action during that time

This is a very common pattern in Portuguese:

• completed event in the preterite
• ongoing background action in the imperfect

So the structure is similar to:

• The worm appeared while I was using the watering can

Yes. In European Portuguese, estar a + infinitive is very common for an action in progress.

So you could say:

• A minhoca apareceu junto ao rebento enquanto eu estava a usar o regador.

That sounds very natural in Portugal.

The difference is mainly one of focus:

• usava = imperfect, more general background past
• estava a usar = more explicitly emphasizes that the action was in progress at that moment

Both are correct here.

Junto a means near, close to, or next to.

In this sentence:

• junto ao rebento = near the sprout / next to the sprout

The form ao is a contraction:

• a + o = ao

So:

• junto a + o rebento → junto ao rebento

Because rebento is a masculine singular noun, and here it comes with the definite article o.

So the preposition a combines with o:

• a + o = ao

This kind of contraction is very common in Portuguese:

• a + o = ao
• a + a = à
• de + o = do
• em + o = no

Here, rebento means a sprout, shoot, or new plant growth.

In European Portuguese, rebento is a normal word in this gardening or plant context.

Be aware that rebento can also mean offspring or child in other contexts, but here the presence of regador and the garden setting make the plant meaning clear.

Regador means watering can.

It comes from the verb regar, which means to water plants.

So:

• regar = to water
• regador = watering can

It is a masculine noun:

• o regador

Not necessarily. Portuguese often leaves out subject pronouns because the verb form already shows who the subject is.

So this is also possible:

• A minhoca apareceu junto ao rebento enquanto usava o regador.

However, keeping eu is helpful here because the main subject of the sentence is a minhoca, and then the subordinate clause switches to I. Including eu makes that change very clear.

So:

• with eu = clearer, slightly more explicit
• without eu = still possible, but a little less clear at first glance

Because enquanto means while, and it highlights that two actions were happening at the same time.

Here:

• the worm appeared
• at the same time, I was using the watering can

Quando means when, and it usually points more to a time point or occasion rather than ongoing simultaneity.

So in this sentence, enquanto is the more natural choice.

Yes. Portuguese allows that very naturally.

For example:

• Enquanto eu usava o regador, a minhoca apareceu junto ao rebento.

This has essentially the same meaning. The difference is mostly in emphasis:

• original order: first the worm’s appearance, then the background context
• reversed order: first the background context, then the main event

Yes, you could.

Compare them:

• junto ao rebento = near / close to / next to the sprout
• ao lado do rebento = at the side of / beside the sprout

Ao lado de can sound a bit more physically specific, while junto a/ao is slightly broader and often a bit more compact in style.

In this sentence, both are natural.

Both exist, and both can be heard. In this sentence, junto ao rebento is perfectly natural and standard.

You may also hear junto do rebento in some contexts, but junto a/ao is very common in careful standard Portuguese, especially in written language.

So for a learner, junto ao rebento is an excellent model to use.

The important part is nh, which is pronounced like the ny sound in canyon.

A rough guide is:

• minhoca ≈ meen-YO-ka

In European Portuguese, the final a is usually weaker than in many other varieties, so it may sound closer to a very soft uh.

The key point is:

• nh = a palatal nasal sound, similar to ny, not a normal English n
  • h combination