Dobrovolníci třídí obuv.

Because dobrovolníci is the nominative plural form of dobrovolník.

• dobrovolník = one volunteer
• dobrovolníci = volunteers

This noun is masculine animate, and in the nominative plural, masculine animate nouns often end in -i.

So in this sentence, dobrovolníci is the subject.

Třídí is the present tense form of the verb třídit.

The present-tense pattern is:

• já třídím = I sort
• ty třídíš = you sort
• on/ona/ono třídí = he/she/it sorts
• my třídíme = we sort
• vy třídíte = you sort
• oni/ony třídí = they sort

A useful thing to notice: in Czech, 3rd person singular and 3rd person plural are often the same form. So třídí can mean:

• he/she/it sorts
• they sort

Here we know it is plural because the subject is dobrovolníci.

There are two main clues:

1. dobrovolníci is in the nominative plural, which is the normal case for the subject.
2. obuv is the thing being sorted, so it functions as the direct object.

In Czech, case endings often show the role of a word more clearly than word order does.

So:

• dobrovolníci = subject
• třídí = verb
• obuv = direct object

Here obuv is in the accusative singular, because it is the direct object of the verb třídí.

A detail that can confuse learners: the form obuv looks the same in both the nominative and accusative singular.

So even though the form does not change, its role in the sentence does:

• Obuv je mokrá. → obuv is nominative (subject)
• Dobrovolníci třídí obuv. → obuv is accusative (object)

In Czech, obuv is usually treated as a singular collective noun, meaning footwear in general.

So Czech often uses:

• obuv = footwear / shoes as a category

rather than a normal plural noun.

If you wanted to talk about individual pairs or specific shoes, Czech might use other words depending on context, but obuv is very natural when speaking generally, especially in formal or practical contexts.

Because grammatical gender in Czech is not determined only by the final letter.

Although many feminine nouns end in -a, some feminine nouns end in a consonant. Obuv is one of them.

So you simply need to learn it as:

• ta obuv = feminine

This is not unusual in Czech. Another common example is:

• dlaň = palm of the hand, also feminine

Yes. Czech word order is more flexible than English word order because case endings help show grammatical roles.

The neutral order here is:

• Dobrovolníci třídí obuv.

But other orders are possible, for example:

• Obuv třídí dobrovolníci.
• Třídí dobrovolníci obuv.

These versions can sound more marked and may shift the focus or emphasis.

For a learner, the original order is the safest and most neutral one: subject + verb + object.

Yes, ř is one of the hardest Czech sounds for English speakers.

A rough pronunciation guide:

• tří- sounds approximately like tree but with Czech ř instead of English r
• -dí sounds like dee

So třídí is roughly třee-dee, but that is only approximate.

About ř:

• It is a special Czech sound, something between r and zh/ž
• Many learners need a lot of practice with it
• It is completely normal not to master it right away

Also note the long vowels:

• í is a long ee sound

So both tří- and -dí have long í.

Třídit is imperfective.

That means it is used for:

• ongoing actions
• repeated actions
• general statements
• processes without focusing on completion

So this sentence presents the action as a process: the volunteers are engaged in sorting footwear.

If Czech wanted to emphasize completion, it would usually use a perfective verb instead, but the exact perfective partner depends on the intended meaning and context.

For basic learning, it is enough to remember:

• třídit = imperfective, to sort / be sorting

It sounds neutral and natural.

A couple of nuances:

• dobrovolníci is a normal everyday word
• obuv is slightly more formal or practical than some more everyday alternatives, because it means footwear as a category

So the sentence could fit contexts like:

• charity work
• aid distribution
• warehouse sorting
• donation centers
• official descriptions of activities

It is not overly formal, but it does have a slightly practical, matter-of-fact tone because of obuv.