Uyku tulumu kamp matının üstünde.

In Turkish, the present-tense to be is often not spoken in simple sentences like this.

So:

• Uyku tulumu kamp matının üstünde. = The sleeping bag is on the camping mat.

Turkish simply leaves is unspoken here.
A more formal or emphatic version can use -dir:

• Uyku tulumu kamp matının üstündedir.

Both are correct, but the version without -dir is very common in everyday Turkish.

These are noun compounds, which are very common in Turkish.

• uyku tulumu = sleeping bag
• kamp matı = camping mat

Turkish often combines two nouns this way:

• the first noun describes the second
• the second noun usually takes a compound ending such as -ı / -i / -u / -ü

So:

• uyku + tulumu
• kamp + matı

You should learn these as whole vocabulary items, not translate them too literally word by word every time.

Because üstünde works in a structure that requires the previous noun to be in the genitive form.

So:

• kamp matı = camping mat
• kamp matının = of the camping mat

The full phrase is:

• kamp matının üstünde

This literally works like:

• on the top/surface of the camping mat

The ending -nın is the genitive ending here.

Üstünde means on it, on top of it, or on its upper side.

It can be broken down like this:

• üst = top, upper part
• üstü = its top
• üstünde = on its top / on it

More technically:

• üst
  • -ü
    • -nde

The -de part is the locative ending, meaning something like in/on/at.
So üstünde is not just a simple one-piece word; it is built from smaller parts.

It functions a bit like that, but not exactly.

In Turkish, words like these are often used:

• üst = top
• alt = bottom, under
• iç = inside
• ön = front
• arka = back
• yan = side

They are really nouns, but they often behave in ways that English speakers think of as prepositions or postpositions.

So kamp matının üstünde is more literally like:

• at the top/surface of the camping mat

That is why the structure looks different from English on the camping mat.

Yes, very often you can.

• kamp matının üstünde
• kamp matının üzerinde

Both can mean on the camping mat.

A rough difference is:

• üstünde can feel a bit more like on top of
• üzerinde can feel a bit more general, like on/upon

In many everyday situations, the difference is small, and both sound natural.

Turkish does not use articles the same way English does.

So this sentence could be translated differently depending on context:

• The sleeping bag is on the camping mat.
• A sleeping bag is on the camping mat.
• sometimes even The sleeping bag is on a camping mat.

English needs a/an/the, but Turkish often leaves that to context.

The given order is the most neutral and straightforward:

• Uyku tulumu kamp matının üstünde.

That is a very natural way to say it.

Turkish word order is more flexible than English, though. You can move parts around for emphasis or style. But in a simple teaching example, this order is the safest one to learn first:

• subject: uyku tulumu
• location/predicate: kamp matının üstünde

These two vowels are important because they do not match normal English spelling.

• ı is a vowel with no exact English equivalent

  • it is a deep, unrounded vowel
  • you can think of it as somewhat like a very plain uh sound, but farther back in the mouth
  • examples here: matının

• ü is like German ü or French u

  • say ee while rounding your lips
  • examples here: üstünde

So in this sentence, those vowels matter a lot:

• matının
• üstünde

If you replace them with English-style i or u, your pronunciation will sound noticeably different to a Turkish speaker.