Explanation
The account relationship is a standard lookup field on an opportunity. A lookup field allows the user to select a record from another object and link it to the current record. The account field on an opportunity allows the user to select an account that the opportunity is related to. The stage relationship is not a lookup field, but a picklist field that indicates the sales stage of the opportunity, such as Prospecting, Negotiation, or Closed Won.
The quote relationship is not a standard lookup field, but a custom lookup field that can be created to link an opportunity to a quote. A quote is a record that shows proposed prices for products and services.

Explanation
A roll-up summary field is the best way to display the sum of all closed won opportunity amounts at the account level. A roll-up summary field is a type of field that calculates a value from a set of related records, such as the sum, average, min, or max. A roll-up summary field can only be created on the master object of a master-detail relationship, and it can only calculate values from the detail object. For example, a roll-up summary field called Total Revenue could be created on the Account object, and it could calculate the sum of the Amount field from the Opportunity object, where the Stage field equals Closed Won. A custom report type is a tool that allows the user to create a report based on the relationships between a primary object and its related objects. A custom report type does not display a value at the account level, but at the report level. The opportunity related list is a component that shows the related opportunities for a specific account record. The opportunity related list does not display the sum of all closed won opportunity amounts, but only the individual amounts for each opportunity.

Explanation
The thing that the associate should do to show that GCC is part of the CK portfolio when creating the CK Account record is to add Get Cloudy Consulting to the Parent Account field. The Parent Account field is a standard field on the Account object that allows the user to link an account to another account that is its parent company. This way, the user can create an account hierarchy that shows the relationships between parent accounts and their subsidiaries. The user can enter the name of the parent account in the Parent Account field when creating or editing an account record. Viewing account hierarchy and selecting Add Child Account or selecting New on the child accounts related list are not the correct actions to show that GCC is part of the CK portfolio, because they are used to create a new account that is a subsidiary of an existing account, not to link an existing account to another existing account.