Explanation:
Graphical user interface Description automatically generated

Box 1: Load the extracted topic into a variable
Power Virtual Agents uses entities to understand and identify a specific type of information from a user's responses. When saving the identified information to a variable, a variable type will be associated with it. The variable type is analogous with the entity.
In Power Virtual Agents, a topic defines a how a bot conversation plays out.
A topic has trigger phrases - these are phrases, keywords, or questions that a user is likely to type that is related to a specific issue - and conversation nodes - these are what you use to define how a bot should respond and what it should do.
Box 2: Create a custom entity
The prebuilt entities cover commonly used information types, but on some occasions, such as when building a bot that serves a specific purpose, you'll need to teach the bot's language understanding model some domain-specific knowledge.
Reference:
https://docs.microsoft.com/en-us/power-virtual-agents/advanced-entities-slot-filling