According to the Salesforce Manufacturing Cloud documentation, to create a new custom metric on the Account product period forecast component, you need to create a custom field on the Account Product Period Forecast object and another custom field on the Account Product Forecast object. Then, you need to map both of these fields in the Account Forecast setting page. This will allow you to add the custom metric to the Forecast tab of an account and track it along with the standard metrics1. Reference: 1: Create Custom Fields for Account Product Forecast and Account Product Period Forecast Objects

It is important to understand the landscape of the business before going into the details of requirements because it helps the consultant to ensure there's an understanding of the big picture and where the real opportunity lies between teams agnostic of Manufacturing Cloud. By analyzing the current state of the business, the consultant can identify the pain points, challenges, goals, and opportunities of the organization and its stakeholders. The consultant can also map out the value chain, the customer journey, the key processes, and the systems and data involved in the business operations. This will help the consultant to align the requirements with the business objectives and priorities, and to design a solution that delivers value and impact across the organization. Understanding the business landscape also enables the consultant to communicate effectively with the client and to establish trust and credibility. Reference:
Manufacturing Cloud - Salesforce
Manufacturing - Salesforce.com
Meet Manufacturing Cloud Unit | Salesforce Trailhead

Explanation
To create a custom metric for display on Agreement Terms, you need to create custom fields on the Sales Agreement Product and Sales Agreement Product Schedule objects and map them using the Custom Metric Mapping tool. However, only number, percent, and currency field types are supported for mapping. You cannot use formula or value field types for this purpose. References: Custom Metric Mapping, Create Custom Metrics for Agreement Terms

Explanation
These three user types can be selected to receive credit for an order in the Tableau CRM configuration wizard when calculating actuals against account manager targets. The configuration wizard guides users through the creation of an app from the Analytics for Manufacturing template and allows them to customize the data and settings for the app. One of the settings is to choose who gets credit for the orders, which determines how the actual revenue is attributed to the account managers. The user can select one of the following options:
Account Owner: This option credits all orders to the account owner's actual revenue, regardless of who owns the order. This is useful when the account owner is responsible for the overall relationship and revenue of the account.
Order Owner: This option credits all orders to the order owner's actual revenue, regardless of who owns the account. This is useful when the order owner is responsible for the individual order and revenue of the order.
Other User: This option credits all orders to a custom user's actual revenue, based on a custom lookup field for a user on the account. This is useful when there is a different user, such as a sales engineer or a partner, who is responsible for the order and revenue of the order.
References: = Create and Share an App from the Analytics for Manufacturing Template, Salesforce Authentication - Tableau, The Configuration Wizard - Salesforce Developers