Learn Russian: Эта инсталляция — просто концептуальный куб. - This installation is simply a conceptual cube.

In Russian, when both the subject (инсталляция) and the predicate (куб) are nouns in the Nominative case, and the present tense verb 'is' is omitted, a dash (тире) is required between them. It acts as a visual substitute for 'is'.

How would I use this lesson's topic to ask 'What kind of installation is this?' before getting this answer?

You would ask: Что это за инсталляция? Remember that что за requires the noun to be in the Nominative case, and if you include the pronoun это, it usually splits the phrase (Что это за...).

If I wanted to exclaim 'What a conceptual cube!' using this lesson's grammar, how would I say it?

You would say: Что за концептуальный куб! Again, что за is followed directly by the Nominative case, making it perfect for exclamations of surprise, admiration, or even bewilderment.

Could I use только instead of просто to mean 'simply' or 'only' here?

Not quite naturally. Просто means 'simply' or 'just' in the sense of 'nothing more than' or 'plainly.' Только strictly means 'only' (e.g., only one cube, not two). Here, просто perfectly emphasizes the unpretentious nature of the art piece.