Uyku tulumunu kamp matının üstünde açtık.

Uyku tulumu is the base form meaning sleeping bag. In this sentence, it is the direct object and it is specific, so Turkish adds the accusative ending.

Because uyku tulumu is a noun compound, the full form becomes uyku tulumunu.

A rough breakdown is:

• uyku = sleep
• tulum-u = bag + compound ending
• -nu = accusative ending after that compound/possessive form

So uyku tulumunu açtık means we opened/unrolled the sleeping bag.

The verb ending tells you.

Açtık breaks down as:

• aç- = open
• -tı- = past tense
• -k = we

So açtık means we opened. Turkish often leaves out subject pronouns like biz when the verb already makes the subject clear.

Yes, the basic meaning is opened, but in context English may translate it more naturally as opened up, spread out, or unrolled.

Turkish often uses açmak for things that English describes with different verbs, such as:

• opening a door
• opening an umbrella
• opening a map
• spreading out bedding or a sleeping bag

So here açtık is very natural Turkish.

This is a very common Turkish structure.

Breakdown:

• kamp matı = camping mat
• kamp matının = of the camping mat
• üstü = its top / upper side
• üstünde = on its top / on top of it

So kamp matının üstünde literally means on the top/surface of the camping mat, which is why it is translated as on the camping mat or on top of the camping mat.

That is the locative ending, which gives meanings like in, on, or at.

Here:

• üstü = its top / upper side
• üstünde = on its top

The n appears because Turkish uses a buffer consonant before case endings after possessive forms.

So this is not a separate word; it is a normal grammatical ending.

These are both Turkish noun compounds.

Turkish often expresses X Y combinations by putting two nouns together and adding a special ending to the second noun:

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

This is extremely common in Turkish. English often just puts one noun before another, but Turkish usually marks the second noun.

Because kamp matı functions as one unit: camping mat.

Once that compound is formed, Turkish adds the genitive ending to the whole compound:

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

So you treat kamp matı as a single noun phrase and then decline it.

Turkish normally puts the verb at the end. A very common neutral pattern is:

subject + object + other information + verb

Here the subject is omitted because it is understood from the verb, so you get:

• Uyku tulumunu = the sleeping bag
• kamp matının üstünde = on the camping mat
• açtık = we opened/unrolled

That makes the sentence sound natural and standard.

Yes. Turkish word order is flexible, and changing it usually changes emphasis rather than the basic meaning.

For example:

• Kamp matının üstünde uyku tulumunu açtık.
  This puts a bit more focus on the location.

• Biz uyku tulumunu kamp matının üstünde açtık.
  This adds emphasis to we.

The original order is a natural neutral choice.

The accusative helps show that the object is specific.

Because the sentence has uyku tulumunu, it usually means a particular sleeping bag: the sleeping bag or that sleeping bag.

If you wanted a sleeping bag, you would more naturally say:

• bir uyku tulumu açtık = we opened/unrolled a sleeping bag

So the accusative is an important clue for definiteness.

Yes, often you can.

Both üstünde and üzerinde can mean on or on top of.

Very roughly:

• üstünde can feel a bit more concrete, like on top/surface of
• üzerinde is very common and slightly more neutral

In this sentence, both would sound natural.