Learn Spanish (Latin America): ¿Qué es esto?

esto is the neutral version of "this." You use it when you are pointing at something unknown and asking what it is. Because you don't know what the object is yet, you can't know if it will be a masculine word requiring este or a feminine word requiring esta.

I often confuse qué and cuál. Why do we use qué here?

In Spanish, you use qué when you are asking for a definition or to identify an unknown object. You use cuál when asking "which one" out of a specific group. Since we are asking to identify a total mystery object, qué is the correct choice.

How would I ask "What are these?" if I am pointing at multiple unknown objects?

The word esto does not have a plural form. If you are pointing at a pile of unknown things, you can still just ask ¿Qué es esto? to mean "What is this stuff?". Alternatively, you can ask ¿Qué son estas cosas? which means "What are these things?".