There are a few different methods to data collection that you should know about.
Common Collection Methodologies
Most companies ask customers directly for data. When someone registers with a website a form is commonly required to be filled out. The company asks for an email address, name, and other demographics like age, gender, and potentially more.
Websites tracking via Cookies and Web Beacons
Email Tracking, Apps, and SDK's
Companies often use email tracking to learn that someone has opened an email, in what location and on what type of device. Similarly, apps are often embedded with SDK's supplied by third party data trackers that are used to source consumer data. This is the most common method for data collection when it comes to mobile devices and Digital Consumption data specifically.