Uno de los cordones de mis zapatillas se soltó en la calle y tuve que atarlo otra vez.

Uno de los + plural noun is the normal way to say one of the... in Spanish.

Here, uno works like one, not like the article a/an. That is why you get uno de los cordones = one of the laces.

If you said un cordón de mis zapatillas, that would mean a shoelace of my trainers, which is possible, but it does not highlight the idea of choosing one item out of the set as clearly as uno de los cordones does.

In this sentence, cordón means shoelace.

More generally, cordón can also mean cord, lace, or a similar string-like object, depending on context. With shoes, los cordones naturally means the shoelaces.

So uno de los cordones is literally one of the laces.

Yes, very much so. In Spain, zapatillas commonly means trainers or sneakers.

A learner should know that this word can vary by region. In other Spanish-speaking countries, zapatillas may mean slippers or another kind of light shoe. In Spain, though, mis zapatillas is a very natural way to say my trainers/my sneakers.

If you want to be extra explicit in Spain, you can also hear zapatillas deportivas.

Because soltarse and soltar are not used in the same way here.

Soltar usually means to release, to let go of, or to loosen something: Solté el cordón = I loosened/released the lace.

But soltarse means that something comes loose or comes undone: El cordón se soltó = The lace came loose.

So the se is important. It shows that the lace itself underwent the change, rather than someone actively loosening it.

Yes. Se desató is also very natural for shoelaces.

There is a slight difference in feel:

Se desató focuses more on becoming untied.
Se soltó focuses more on coming loose.

With a shoelace, both can work. If you want to stress that the knot actually came undone, se desató may be more exact. If you just mean the lace loosened and you needed to tie it again, se soltó sounds very good.

Because it describes a single completed event in the past.

The sentence tells a short sequence: the lace came loose, and then the speaker had to tie it again.

That kind of event is normally expressed with the preterite in Spanish: se soltó, tuve que.

If you used the imperfect, such as se soltaba, it would sound more like a repeated or ongoing situation, not one specific incident.

Because -ó is the normal written ending for the third person singular preterite of -ar verbs.

So: solté = I loosened / I let go
soltaste = you loosened
soltó = he/she/it loosened, or in this case came loose with se

The accent mark shows the stress falls on the last syllable: sol-TÓ.

En la calle gives the idea of location: this happened in the street / out on the street.

Por la calle often emphasizes movement along or through the street, like walking down the street.

In this sentence, the main point is where the event happened, not the movement, so en la calle is a very natural choice.

Tuve que means I had to in the sense of a specific necessity that came up and was dealt with.

That is exactly what happens here: the lace came loose, so the speaker had to tie it again.

Tenía que often suggests:

• a background obligation
• something habitual
• something you were supposed to do

So here tuve que atarlo fits better because it refers to one concrete situation.

Atarlo is atar + lo.

Atar means to tie.
Lo means it.

So atarlo means to tie it.

The pronoun lo refers to uno de los cordones, understood as el cordón, which is masculine singular. That is why the pronoun is lo, not la.

Yes. Both are correct:

Tuve que atarlo
Lo tuve que atar

With tener que + infinitive, object pronouns can usually either:

• attach to the infinitive, or
• go before the conjugated verb

In everyday Spanish, tuve que atarlo is very common and sounds completely natural.

Yes, you could.

Otra vez means again or once again, and it is extremely common in everyday speech.

De nuevo also means again, and can sound a little more neutral or slightly more formal depending on context.

So both work: tuve que atarlo otra vez
tuve que atarlo de nuevo

Because the lace belongs to your pair of trainers/shoes, which is naturally expressed in the plural.

Spanish, like English, often refers to footwear as a pair in the plural: mis zapatos, mis botas, mis zapatillas.

So uno de los cordones de mis zapatillas simply means one of the laces from your trainers. If you wanted to be extra specific, you could say uno de los cordones de una de mis zapatillas, but that is less natural unless the exact shoe matters.