Çöp torbası kampçı ünitesinde kaldı.

It breaks down like this:

• çöp torbası = the subject
• kampçı ünitesinde = the location phrase, meaning in the camper unit
• kaldı = the verb, in the past tense

So the overall pattern is:

subject + place + verb

That is very normal in Turkish, and the verb commonly comes at the end.

Because Turkish often uses a noun compound where English uses two nouns together.

Here:

• çöp = trash, garbage
• torba = bag
• çöp torbası = trash bag

In this kind of compound, the second noun usually takes -(s)ı / -(s)i / -(s)u / -(s)ü.

So:

• çöp torba = not correct here
• çöp torbası = correct

This pattern is very common:

• kahve fincanı = coffee cup
• otobüs durağı = bus stop
• yatak odası = bedroom

This word group has a few layers:

• kampçı = camper / camping person
• ünite = unit
• kampçı ünitesi = camper unit / unit for campers
• kampçı ünitesinde = in the camper unit

More technically, ünitesinde can be divided like this:

• ünite = unit
• -si = the compound/possessive-type ending
• -n- = a buffer consonant
• -de = locative ending, meaning in / at / on

So:

ünite + si + n + de = ünitesinde

That -n- is a buffer consonant.

When a noun already has the 3rd-person possessive / compound ending and then you add a case ending, Turkish often inserts -n- to connect them smoothly.

For example:

• evi → evinde = in his/her/its house
• arabası → arabasında = in his/her/its car
• ünitesi → ünitesinde = in its unit

So the n is not a separate meaning word. It is just part of the normal grammatical connection.

Kaldı is the past tense of kalmak.

Depending on context, kalmak can mean:

• stay
• remain
• be left behind

So in this sentence, kaldı can naturally be understood as:

• stayed
• remained
• was left

Also, kal-dı shows the past tense suffix -dı. The form changes by vowel harmony, so after kal-, you get kaldı, not kaldi.

Not exactly.

Kalmak is usually intransitive. It describes the thing that remains somewhere.

So:

• Çöp torbası kampçı ünitesinde kaldı.
  = The trash bag remained / was left in the camper unit.

If you want to say that someone left it there, Turkish often uses bırakmak instead:

• Çöp torbasını kampçı ünitesinde bıraktı.
  = He/she left the trash bag in the camper unit.

So kaldı focuses on the result or state, not the person doing the action.

Because kalmak is not a verb that takes a direct object in this meaning. The thing that stays/remains is the subject.

Also:

• kampçı ünitesinde has the locative ending -de, so it is clearly the place
• çöp torbası is the thing being talked about
• there is no accusative ending on çöp torbası

So the sentence is about the trash bag and where it ended up.

Turkish usually does not use articles the way English does.

So a bare noun can mean:

• a trash bag
• the trash bag

The exact meaning depends on context.

If Turkish wants to make a / one more explicit, it can use bir:

• bir çöp torbası = a trash bag / one trash bag

But in your sentence, Turkish simply leaves that to context.

Yes. Turkish word order is fairly flexible.

The version you have is natural and neutral:

• Çöp torbası kampçı ünitesinde kaldı.

But you could also say:

• Kampçı ünitesinde çöp torbası kaldı.

That puts a bit more attention on the location.

In ordinary statements, the verb usually stays at the end, but other parts can move around for emphasis or topic.

-çı / -ci / -cu / -cü is a very common Turkish suffix. It often means:

• a person associated with something
• someone who does something
• someone involved with something

So:

• kamp = camp
• kampçı = camper / camping person / camping enthusiast

This suffix appears in many everyday words:

• balıkçı = fisherman / fish seller
• kahveci = coffee seller / café owner
• sporcu = athlete

Here, kampçı is used before another noun to help describe the type of unit.

A few letters here are especially important for English speakers:

• ç = like ch in chair
• ö = say e as in bed, but with rounded lips
• ü = say ee as in see, but with rounded lips
• ı = the dotless i; roughly like a relaxed vowel in sofa, but farther back in the mouth

So very roughly:

• çöp ≈ churp / chœp
• torbası ≈ tor-bah-suh
• ünitesinde ≈ ü-ni-te-sin-de
• kaldı ≈ kal-duh

Those are only rough guides, but they can help at first.