An Asset is an area or device within a location that holds Sensors and Controllers.
This is a compulsory element that you will need to set up before adding any Sensors or Controllers. Like a Location an Asset is a great tool to help you further group Sensors and Controllers to allow for deeper analysis of the data collected.
Using the map functionality you will be able to precisely define the position of your Asset for greater accuracy.
It is up to you how you choose what is a Location versus an Asset (you can read more about Location here) as this should be based on how you want to use the data in future. Examples of an Asset include a door, irrigation gate or a section of your Location (e.g a floor of a multistory building).