Standards are agreed ways of doing things. They may specify the exact physical and/or electronic dimensions and behaviors of something, such as standards for USB-C connections or the Bluetooth communication standard. Building codes give requirements, including materials, dimensions, and methods, for erecting safe buildings. Other standards may specify correct procedures for an activity.
Sources of Standards:
Standards are created by many different groups. Companies in an industry may come together to create industry standards. Other standards are created by governmental or quasi-governmental organizations. Professional organizations are also often involved in creating standards. Many times, such groups will work with large standards organizations such as ISO (International Organization for Standards) or ANSI (American National Standards Institute) to publish the standards. In many cases, there is a cost to acquiring a standard.
The best way to find out about the existence of a standard relevant to your subject is by reading research articles, handbooks, and other works on the subject. Check to see whether they mention standards in their text or references.
Here's some to get you started: