An interrogative sentence asks a direct question and is punctuated at the end with a question mark. It is one of the four basic types of sentences, and it's a highly useful one. Could you imagine life without questions?
Interrogative sentences allow you to gather information and clear up confusion as well as engage in interesting conversations with others. It's also useful in writing as an organizational tool; for example, you can set up questions as headers and answer them to explain a concept in more detail in expository writing.