الجهاز ده مستعمل، مش جديد.

In Egyptian Arabic, demonstratives like ده usually come after the noun.

So:

• الجهاز ده = this device
• literally, it looks like the device this

That is normal Egyptian word order.
In Standard Arabic, you would more often see هذا الجهاز, with this first.

Here, ده means this and matches the noun الجهاز, which is masculine singular.

A few useful pairs are:

• ده = this, masculine
• دي = this, feminine

So:

• الجهاز ده = this device
• العربية دي = this car

In everyday Egyptian, ده can sometimes feel a bit flexible and may be translated as this or that depending on context, but here this device is the natural reading.

Yes. In Arabic, the present-tense is/are is usually not said in sentences like this.

So:

• الجهاز ده مستعمل literally looks like this device used
• but it means this device is used

The same thing happens in the second part:

• مش جديد = not new

There is no separate word for is in the present tense here.

مش means not.

It negates what comes after it. In this sentence, it negates the adjective جديد:

• جديد = new
• مش جديد = not new

In Egyptian Arabic, مش is very common with adjectives, nouns, and similar non-verbal predicates.

Yes, they are closely related, and that is exactly why the sentence sounds natural.

It is like saying:

• It’s used, not new.

The first part gives the description.
The second part makes the contrast explicit and removes any doubt.

This kind of double phrasing is very common in everyday speech for emphasis and clarity.

مستعمل means used or second-hand.

It is commonly used for things like:

• phones
• cars
• appliances
• devices

So الجهاز ده مستعمل means the device is not brand-new; it has been used before.

It does not simply mean busy or in use here. In this context, it clearly means used / second-hand.

Because جديد here is a predicate adjective, not an adjective directly attached to the noun inside the noun phrase.

Compare these:

• الجهاز الجديد = the new device
• الجهاز ده جديد = this device is new

In الجهاز الجديد, new is part of the noun phrase, so it takes ال because the noun is definite.

But in الجهاز ده مش جديد, جديد is the thing being said about the device, so it does not take ال.

Because الجهاز is a masculine singular noun, and adjectives agree with it.

So you get:

• الجهاز ده مستعمل، مش جديد
  masculine singular

If the noun were feminine, the adjectives would usually be feminine too:

• العربية دي مستعملة، مش جديدة
  = This car is used, not new.

So the adjective form changes to match the noun.

In Egyptian Arabic, ج is usually pronounced like g in go, not like the English j in job.

So:

• الجهاز sounds roughly like el-gihaaz or el-gehaaz
• جديد sounds roughly like gedeed

This g sound is one of the most noticeable features of Egyptian Arabic pronunciation.

Yes, you can, but it changes the feel a little.

• الجهاز مستعمل = the device is used
• الجهاز ده مستعمل = this device is used

Including ده makes it more conversational and more clearly points to a specific device in front of you or already known in the conversation.

So the version with ده is very natural in spoken Egyptian.

Yes, this is natural Egyptian Arabic.

A Standard Arabic version would be something like:

• هذا الجهاز مستعمل، ليس جديدًا

The biggest differences are:

• Egyptian uses ده after the noun
• Egyptian uses مش for not
• Standard Arabic uses هذا and ليس

So the sentence you were given is the everyday Egyptian way to say it.