Why computer understand 0 and 1?

A bit. Logical and or. Switch on or off. Answer yes or no.

A bit
Each 1 or 0 used in the representation of computer data can be used to present information to you, in order that you may learn it, especially the syntax and forms of the English language, so that when you present questions to global forums where computers also interpret the 1's & 0's to present to people, your question will be understood by those experts whose assistance you so plainly require.