Ons ruil die kledingstuk uit.

Because uitruil works as a separable verb in Afrikaans.

In a normal main clause, the finite verb goes near the front, and the separable part moves to the end:

• Ons ruil die kledingstuk uit.

But in other structures, the verb often stays together:

• Ons wil die kledingstuk uitruil.
• ... dat ons die kledingstuk uitruil.

So the uit at the end is not random; it belongs to the verb.

It can mean both.

Afrikaans uses ons for both the subject and the object form:

• Ons ruil die kledingstuk uit. = We exchange the garment.
• Hulle sien ons. = They see us.

In your sentence, it means we because it is the subject.

Because regular Afrikaans verbs do not change for person the way English verbs sometimes do.

So you get:

• ek ruil
• jy ruil
• hy/sy ruil
• ons ruil
• julle ruil
• hulle ruil

That is much simpler than English, where you have forms like I trade but he trades.

Here die means the.

A useful thing to know is that Afrikaans uses die for:

• singular nouns
• plural nouns
• all grammatical genders

So die does not tell you by itself whether the noun is singular or plural. The noun does that:

• die kledingstuk = the garment
• die kledingstukke = the garments

Yes, it is correct, but it sounds a bit more formal or retail-like than some everyday alternatives.

kledingstuk means garment or item of clothing. In casual speech, people might more often say:

• klere = clothes
• or the specific item, like hemp, broek, rok, etc.

So kledingstuk is perfectly fine, but it is a slightly more formal vocabulary choice.

No. Afrikaans often uses the simple present where English might use either:

• we exchange
• we are exchanging

So Ons ruil die kledingstuk uit can work naturally without any extra word for are.

If you really want to stress that the action is in progress, Afrikaans can use a construction like:

• Ons is besig om die kledingstuk uit te ruil.

But that is not necessary in an ordinary sentence.

Sometimes ruil by itself can mean trade or swap, so it is not impossible as a verb.

However, in this sentence, uit is part of the intended verb pattern, so if you are learning this exact structure, keep it:

• Ons ruil die kledingstuk uit.

Leaving uit out may change the feel or make the sentence less like the version you were taught.

They are related, but not always identical in use.

A helpful rule of thumb is:

• omruil is very common for exchanging an item for another one, especially in a shop
• uitruil often has more of a swap/exchange between parties or swap out feel

So depending on context, many speakers might also say:

• Ons ruil die kledingstuk om.

If the situation is a store exchange, omruil is especially worth learning.

Afrikaans usually forms the past with het plus a past participle.

So:

• Ons het die kledingstuk uitgeruil.

Notice that the separable verb becomes one word in the participle:

• uitruil → uitgeruil

That pattern is very common with separable verbs in Afrikaans.

Then the separable verb usually stays together.

For example:

• Ons wil die kledingstuk uitruil. = We want to exchange the garment.
• Ek weet dat ons die kledingstuk uitruil. = I know that we are exchanging the garment.

So a useful contrast is:

• main clause: Ons ruil die kledingstuk uit.
• modal/subordinate structure: ... uitruil

That is an important word-order pattern to get used to in Afrikaans.