When designing steps with operations requiring variables, it is best practice to query targets for variables1.
This allows you to dynamically obtain the values of the variables from the target devices, rather than hard coding them or using scalar variables that may not reflect the current state of the target. Querying targets for variables also enables you to design for a dynamic environment, where the target configuration may change over time.
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1: Define discovery steps

SNMP credentials are used by Discovery to communicate with devices that support the Simple Network Management Protocol (SNMP). SNMP credentials do not include a user name, just a password, called the community string. The default read-only community string for many SNMP devices is public, and Discovery will try that automatically. Enter the appropriate SNMP credentials if they differ from the public community string1.
1: SNMP credentials - Product Documentation: Utah - Now Support Portal

The Extension section in a horizontal pattern is executed after the Identification sections have completed and the CI has been identified. The Extension section allows adding additional attributes or relationships to the CI, or launching other patterns for further discovery12.
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1: ITOM: Extending Discovery/Service Mapping Patterns - GlideFast ServiceNow
2: Horizontal Pattern probe - Product Documentation: San Diego - ServiceNow

Hardware Models are templates that define the attributes and default values for a specific type of hardware configuration item (CI). Hardware Models can have a one-to-many relationship with the following entities:
* Assets: An asset is a tangible or intangible resource that is tracked and managed by the organization, such as a laptop, a license, or a contract. A Hardware Model can be associated with multiple assets that share the same characteristics and specifications.
* Configuration Items: A CI is any component that needs to be managed in order to deliver an IT service, such as a server, an application, or a user. A Hardware Model can be associated with multiple CIs that share the same characteristics and specifications.
* Model Categories: A model category is a classification of Hardware Models based on their function, such as network, storage, or server. A Hardware Model can belong to one or more model categories that define its scope and usage.
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Hardware Model
Asset
Configuration Item (CI)
[Model Category]

Credential affinity is an association between a set of credentials and a device on your network. When Discovery or Orchestration first attempts to access a device, they try all available credentials until a valid one is found. Once a valid credential is found, it is recorded in the dscy_credentials_affinity table, and further discovery processes rely on this information. If the credentials are modified or changed, the process will be repeated until a valid credential is found and updated in the same table. Credential affinity allows Discovery to use the most efficient and successful credential for each device, and avoid unnecessary credential failures.
1: Credential affinity for Discovery and Orchestration, Credential Management in ServiceNow discovery