"I want to have a television."

Translation: Θέλω να έχω τηλεόραση.

[Anas276]

What's the difference between "μία" and "μια"?

[Raftus]

So it's ok to omit the article, is it? I didn't know you could do that in Greek.

[Kadmos_Thebes]

You can either omit it or say it, but NOT stress it when speaking, to avoid confusion with "one," which would again be μία. If you put it, you must stress the word τηλεόραση again. Most of the time we drop it, though.
Θέλω να έχω (μια) τηλεόραση κι εγώ όπως όλοι οι άνθρωποι!

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μια is the same word as μία (a, one) except that we pronounce it in one syllable, not two

[StefanMorris]

"Θέλω μία τηλεόραση" is not okay?

[D_..]

No, because you've not included "to have".