Learn Turkish: Bu mucize sadece kullanışlı değil, aynı zamanda çok ucuz. - This miracle is not only practical, but also very cheap.

In Turkish, değil (not) comes right after the adjective or noun it negates. So instead of 'not only practical', Turkish structures it as 'only [practical not]' (sadece kullanışlı değil). This word order is standard for this grammar pattern.

The lesson topic includes an optional (da) in this pattern. Where would it go if we wanted to use it here?

If you wanted to add it, it would go at the very end of the sentence: ...aynı zamanda çok ucuz da. Adding da (or de) gives a little extra emphasis to the second point, but as you can see in this sentence, it is completely optional and often left out.

Does aynı zamanda literally mean 'but also'?

Literally, aynı zamanda means 'at the same time' (aynı = same, zaman = time, -da = in/at). In Turkish, pairing 'only X not' with 'at the same time Y' is the standard conversational way to express the English idea of 'not only X, but also Y'.

How is the word kullanışlı (practical) built from the verb kullanmak (to use)?