How do you use index in Word?

Could you elaborate on how one might effectively utilize the index feature in Microsoft Word? I'm curious about the steps involved in creating an index, as well as any tips or tricks for making it more user-friendly and informative. Is it necessary to mark each entry manually, or does Word offer automated tools to assist with the process? Furthermore, how does one customize the appearance of the index to align with the overall design and style of the document? I'm looking for a comprehensive overview of the index feature in Word, including its benefits and limitations.