guìtái zài nàbiān.

In this sentence, 在 means to be located at / to be in / to be at.

So 柜台在那边 means the counter is located over there.

This is one of the most basic ways to say where something is in Chinese:

thing + 在 + place

Examples:

• 书在桌子上。 = The book is on the table.
• 洗手间在那边。 = The restroom is over there.

Because 是 is usually used to connect one noun to another noun, like A is B.

Examples:

• 我是老师。 = I am a teacher.
• 这是柜台。 = This is the counter.

But for location, Chinese normally uses 在, not 是.

So:

• 柜台在那边。 = correct
• 柜台是那边。 = not correct for location

The pattern is:

subject + 在 + location

So here:

• 柜台 = the counter
• 在 = is located at
• 那边 = over there

That gives: 柜台 在 那边。

This is very natural Chinese word order for saying where something is.

那边 literally means that side, but in everyday Chinese it often means over there.

It usually has a slight feeling of direction or distance, often as if someone is pointing.

So if a store clerk says 柜台在那边, they probably mean The counter is over there, possibly with a gesture.

All three can often be translated as there, but they are not exactly the same.

• 那边 = over there / that side
  Slightly more directional
• 那里 = there
  More general
• 那儿 = there
  Colloquial spoken form of 那里, especially common in northern Mandarin

So these are all possible:

• 柜台在那边。
• 柜台在那里。
• 柜台在那儿。

They are all natural, but 那边 can feel a bit more like over that way.

It is pronounced guìtái.

Tones:

• 柜 = 4th tone, guì
• 台 = 2nd tone, tái

So the tone pattern is:

4th tone + 2nd tone

A rough English approximation is something like gway-tie, but the real Mandarin sounds are more precise than that.

柜台 is a general word for a service or sales counter, such as in:

• a shop
• a bank
• a hotel
• a service area

Depending on context, English might translate it as:

• counter
• service desk
• front desk

But it does not always specifically mean a cashier counter. For that, Chinese often uses a more specific word like 收银台.

Yes, absolutely.

柜台在那儿。 is a very natural alternative and means basically the same thing.

The difference is:

• 那边 = a bit more directional, like over there
• 那儿 = simply there

So if someone is pointing, 那边 can feel especially natural.

No. You do not need 的 in 柜台在那边。

This is a complete location sentence, so 的 is unnecessary.

You would use 的 if you were modifying a noun, for example:

• 那边的柜台 = the counter over there

But your original sentence is not a noun phrase. It is a full sentence saying where the counter is.

Not in this sentence as written.

A bare noun like 柜台 can be the subject of a sentence:

• 柜台在那边。

If you want to be more specific, you could say:

• 那个柜台在那边。 = That counter is over there.
• 一个柜台在那边。 = A counter is over there.

But when you use a number or 个, then you need a measure word:

• 一个柜台
• 那个柜台

The most common ways are:

• 柜台在哪儿？
• 柜台在哪里？

Both mean Where is the counter?

If you specifically want to ask which side it is on, you could say:

• 柜台在哪边？

That sounds a little more like Which side is the counter on?