Quando soffia il vento, il ramo del piccolo albero si muove.

In this sentence, quando introduces a time clause meaning when or whenever. Italian often uses the present tense in both parts of the sentence to talk about something habitual or generally true:

• Quando soffia il vento, il ramo del piccolo albero si muove.

This does not have to mean one single event happening right now. It can also mean a general fact: whenever the wind blows, the branch moves.

Both are correct.

• Il vento soffia = the more straightforward, neutral order
• Soffia il vento = a different word order, often used for rhythm, style, or emphasis

Italian word order is more flexible than English word order. In this sentence, putting the verb before the subject sounds natural and a little more literary or descriptive.

So:

• Quando soffia il vento...
• Quando il vento soffia...

are both grammatical.

The comma separates the introductory quando clause from the main clause:

• Quando soffia il vento, = subordinate clause
• il ramo del piccolo albero si muove. = main clause

In English, you often do the same thing when a when clause comes first:

• When the wind blows, the branch moves.

So the comma here is very natural.

Soffia is the third-person singular present of soffiare.

So it can mean:

• he/she blows
• it blows

Here the subject is il vento, so soffia means blows.

A few present-tense forms of soffiare are:

• io soffio
• tu soffi
• lui/lei soffia
• noi soffiamo
• voi soffiate
• loro soffiano

Italian uses definite articles more often than English does.

In this sentence:

• il vento = the wind
• il ramo = the branch
• il piccolo albero = the small tree

Even when English might sometimes sound more general without repeating the, Italian often keeps the article. With natural things like vento, this is especially common.

So an English speaker may feel there are “too many” articles, but in Italian this is normal.

Del is the contraction of di + il.

• di = of
• il = the
• del = of the

So:

• il ramo del piccolo albero = the branch of the small tree

This kind of contraction is very common in Italian:

• di + il = del
• di + lo = dello
• di + la = della
• di + i = dei
• di + gli = degli
• di + le = delle

Italian adjectives often do come after the noun, but some common adjectives can also go before it, especially short everyday ones like piccolo, grande, bello, buono.

So both of these are possible:

• il piccolo albero
• l’albero piccolo

But they do not always feel exactly the same.

In many cases, putting piccolo before the noun sounds more natural and general:

• il piccolo albero = the small tree

Putting it after the noun can sound more contrastive or specific in some contexts:

• l’albero piccolo = the small tree, as opposed to a bigger one

In this sentence, il piccolo albero is the most natural choice.

Si muove comes from the verb muoversi, which means to move, to move oneself, or to sway.

So:

• si muove = moves / is moving / sways

The si is part of the verb. English often just says moves, but Italian commonly uses the pronominal form muoversi for something that moves on its own.

Compare:

• muovere qualcosa = to move something
• muoversi = to move oneself / to move

So here:

• il ramo si muove = the branch moves

That is why si is needed.

Muove is the third-person singular present of muovere or, in this sentence, the pronominal verb muoversi.

Its subject is il ramo, which is singular, so the verb must also be singular:

• il ramo si muove = the branch moves

Some related forms are:

• io mi muovo
• tu ti muovi
• lui/lei si muove
• noi ci muoviamo
• voi vi muovete
• loro si muovono

Italian usually does not need subject pronouns unless you want emphasis or contrast.

The verb endings already show the person, and in this sentence the actual subjects are stated as nouns:

• il vento
• il ramo

So there is no need to add a pronoun.

In fact, using a subject pronoun here would usually sound unnecessary.

Yes. That version is completely correct and probably feels more straightforward to an English speaker because the subject comes before the verb:

• Quando il vento soffia, il ramo del piccolo albero si muove.

The original version:

• Quando soffia il vento, il ramo del piccolo albero si muove.

is just a different word order. The meaning stays the same.

It can suggest either one, depending on context.

In a sentence like this, with the present tense and a general statement, quando often has the sense of whenever:

• Whenever the wind blows, the branch moves.

But in many cases English still translates it simply as when. The exact nuance comes from context, not from a different Italian word.

Most naturally, it sounds like a general truth or a repeated situation.

Because both verbs are in the present tense:

• soffia
• si muove

the sentence suggests something that regularly happens: when the wind blows, the branch moves.

If you wanted to make it clearly about one specific past event, Italian would normally use past tenses instead.