Ovaj paket ima deset gigabajta.

Ovaj means this.

It is the masculine singular nominative form, and it has to agree with paket, which is a masculine singular noun.

So:

• ovaj = masculine
• ova = feminine
• ovo = neuter

Examples:

• ovaj paket = this package/plan
• ova tarifa = this tariff/plan
• ovo selo = this village

Paket is in the nominative singular.

It is the subject of the sentence, so Croatian uses the nominative case here. The basic dictionary form of the noun is also paket.

In this sentence:

• ovaj paket = the subject
• ima = the verb
• deset gigabajta = what the package has

Ima is the 3rd person singular present tense of imati = to have.

Croatian uses imati very naturally for things like plans, packages, subscriptions, and offers. So ima here can mean:

• has
• includes
• comes with

A few present-tense forms of imati:

• ja imam = I have
• ti imaš = you have
• on/ona/ono ima = he/she/it has

So ovaj paket ima... is completely natural Croatian.

After the number deset (ten), Croatian uses the noun in the genitive plural.

So:

• deset gigabajta = ten gigabytes

The basic noun is gigabajt.
Its regular nominative plural is gigabajti, but that form is not used after deset.

Useful comparison:

• jedan gigabajt = one gigabyte
• dva gigabajta = two gigabytes
• deset gigabajta = ten gigabytes

With gigabajt, the form gigabajta appears after both 2, 3, 4 and 5+, so the pattern is a bit harder to notice just from this word alone.

Usually no, not in this kind of sentence.

In everyday Croatian, paket can mean a literal package/parcel, but in telecom and commercial contexts it often means:

• a plan
• a bundle
• a package of services

So Ovaj paket ima deset gigabajta most likely means something like a mobile or internet plan that includes 10 GB of data.

Because Croatian does not have articles like English the and a/an.

That means Croatian usually relies on:

• context
• word order
• demonstratives like ovaj = this

So:

• Ovaj paket ima deset gigabajta = This package/plan has ten gigabytes
• Paket ima deset gigabajta could mean The package has ten gigabytes or A package has ten gigabytes, depending on context

Yes. Croatian word order is more flexible than English word order.

The sentence Ovaj paket ima deset gigabajta is a neutral, natural way to say it.

Other possible versions:

• Paket ima deset gigabajta.
  Natural if you do not need this.
• Deset gigabajta ima ovaj paket.
  Possible, but it sounds more emphatic or contrastive, as if you are stressing the amount.

So the original sentence is probably the best default version for a learner.

A rough English-friendly pronunciation is:

• Ovaj ≈ OH-vai
• paket ≈ PA-ket
• ima ≈ EE-ma
• deset ≈ DE-set
• gigabajta ≈ gee-ga-BYE-ta

A rough full version: OH-vai PA-ket EE-ma DE-set gee-ga-BYE-ta

Two helpful pronunciation notes:

• Croatian j sounds like English y in yes
• Croatian spelling is quite phonetic, so words are usually pronounced much like they are written