Что это? = What is this?
Что это такое? = What is this?
What is the difference between these 2 questions?
Very often these two questions are interchangeable. The word такое adds a little bit more curiosity to the question.
But there is another phrase that could be very useful to memorize.
Что такое лампа? = What does лампа mean?
The reply can be:
Лампа - это lamp.
This is a very simple word, so the person should be a real beginner is he/she asks that. Therefore the best answer is just to translate the word лампа into English.
On the higher level you can explain the word using Russian or just point at the object.
The question Что это такое? can also be used in more aggressive way .
Что это такое? Почему ты повышаешь голос? = What is that? Why are you raising your voice?