Learn Russian: Моё место где-то около пятого ряда.

They are in the Genitive case because they follow the preposition около, which is the focus of this lesson and means near or around. The masculine noun ряд (row) becomes ряда, and the ordinal number пятый (fifth) must match its case and gender, changing to пятого.

Why is где-то used here instead of где-нибудь?

The word где-то means somewhere, referring to a real, existing place that the speaker just isn't exactly sure about. Где-нибудь means anywhere at all, as in when you don't care about the specific location. Since the assigned seat exists in one specific real-world location, где-то is the correct choice.

How is the letter г pronounced in the word пятого?

It is pronounced like an English v. In Russian, the Genitive masculine and neuter adjective endings -ого and -его are always pronounced with a v sound instead of a g. Because ordinal numbers like пятый take adjective endings, they follow this pronunciation rule too.

Does the word место specifically mean seat?

The word место literally translates to place or space. However, in contexts involving tickets, theaters, or public transport, it is the standard Russian word used to mean seat.