Silah masanın üstünde.

• silah = gun / weapon
• masa-nın = of the table
• üst-ü-nde = on its top / on top of it

So the whole sentence literally comes out as something like:

The gun [is] on the table.

A more literal gloss would be:

Gun table-of top-its-on.

That sounds strange in English, but it reflects how Turkish builds the phrase.

In Turkish, the present-tense to be is often not said as a separate word in simple statements like this.

So:

Silah masanın üstünde.
naturally means
The gun is on the table.

There is no separate word for is here, but the sentence is still complete.

If you wanted a different tense, you would usually see extra marking:

• Silah masanın üstündeydi. = The gun was on the table.
• Silah masanın üstünde değil. = The gun is not on the table.

You may also sometimes see -dir in formal or emphatic style, but it is not needed in normal everyday speech.

Because Turkish uses a possessive-style structure here.

masanın üstü literally means the top of the table.

So:

• masa = table
• masanın = of the table

Turkish often expresses locations like on, under, in front of, behind, inside using a noun plus endings rather than a simple preposition.

That is why on the table is built as:

table + of + top + on

So masanın is necessary in standard Turkish.

üstünde can be broken down like this:

• üst = top, upper side, surface
• -ü = its (3rd person possessive ending)
• -nde = in/on/at, with a buffer n before the case ending

So:

üstünde = on its top / on top of it

In the full phrase masanın üstünde, the it refers to the table.

So the structure is literally:

the table's top-on
which English expresses as
on the table

This is a very common Turkish pattern called a genitive-possessive construction.

Pattern:

X-in Y-si = the Y of X

Here:

• masa-nın = of the table
• üst-ü = its top

Together:

masa-nın üst-ü = the top of the table

Then the locative ending is added:

masa-nın üst-ü-nde = on the top of the table

This same pattern appears in many everyday location expressions:

• evin önünde = in front of the house
• kutunun içinde = inside the box
• arabanın arkasında = behind the car
• sandalyenin altında = under the chair

So this sentence is using a very important Turkish structure.

Yes. The locative ending changes by vowel harmony and consonant voicing.

The basic forms are:

• -de
• -da
• -te
• -ta

In üstünde, the vowel before it is front (ü), so -de is the matching form.

That is why you get:

• evde = at home
• okulda = at school
• masada = on/at the table
• üstünde = on top of it

So the form is not random; it follows Turkish sound harmony rules.

Turkish does not have articles like English a and the.

So silah can mean:

• a gun
• the gun
• sometimes just gun/weapon in a general sense

The exact meaning comes from context.

In this sentence, if the meaning shown to the learner is The gun is on the table, that is perfectly fine. Turkish leaves that distinction to context much more than English does.

Not exactly.

Silah masanın üstünde.
usually means something like:
The gun is on the table.

This is good when the gun is already known in the conversation, and you are saying where it is.

Masanın üstünde bir silah var.
means:
There is a gun on the table.

This is better when you are introducing the gun as new information.

So the difference is largely about information structure:

• Silah masanın üstünde. = talking about the gun, giving its location
• Masanın üstünde bir silah var. = introducing the fact that a gun exists there

Turkish word order is flexible, but different orders can sound more natural in different situations.

Silah masanın üstünde. is a very natural sentence meaning The gun is on the table.

But Turkish often shifts word order for emphasis or topic:

• Silah masanın üstünde. = The gun is on the table.
• Masanın üstünde silah var. = There is a gun on the table.

These are not just scrambled versions of the same sentence; the choice affects what sounds like old information and what sounds like new information.

So yes, word order can change, but not always without changing the feel of the sentence.

Not exactly. English uses a preposition: on. Turkish often uses what are sometimes called location nouns or postposition-like nouns.

So üst is really more like top/upper part than a pure preposition.

That is why Turkish says things like:

• masanın üstünde = on the table
• masanın altında = under the table
• masanın yanında = next to the table
• masanın içinde = inside the table / in the table

This is a very Turkish way of expressing location: not usually with one simple preposition, but with a noun-like element plus endings.

Not always. silah can mean weapon in a broader sense, depending on context.

For example:

• in some contexts, silah = gun
• in others, it may mean weapon more generally

So the exact English translation depends on the situation. If your lesson gives gun, that is a normal and common translation here.