Explanation
Master-detail lookup is a type ofrelationship field that can be used to create a relationship between Account and Shoe and prevent orphaned Shoe records. Master-detail lookup establishes a parent-child relationship between two objects, where the parent record controls certain behaviors ofthe child record, such as security, ownership, and deletion. If the parent record is deleted, all the child records are deleted as well.
References:https://help.salesforce.com/s/articleView?id=sf.relationships_considerations.htm&type=5

Explanation
To route new leads to the correct sales person based on the lead address, the administrator should use lead assignment rules that specify criteria based on lead fields such as City, State/Province, or Country, and assign leads that match those criteria to queues or users. Lead assignment rules can be triggered automatically when leads are created or manually by users. Creating a formula field, assigning with an escalation rule, or configuring a validation rule will not route leads to sales people. References:
https://help.salesforce.com/s/articleView?id=sf.leads_assignment_rules.htm&type=5

Explanation
My Domain is a feature that allows administrators to create a custom domain name for their Salesforce org that replaces their instance URL (such as na35.salesforce.com). My Domain provides benefits such as improved security; enhanced branding; faster navigation; access to Lightning components; etc. However, one of the considerations when enabling My Domain is that it changes how users log in to Salesforce - instead of using their instance URL login (such as login.salesforce.com), they have to use their My Domain login (such as mydomain.my.salesforce.com). This applies to all internal and external users who access Salesforce via web browser or mobile app. References:
https://help.salesforce.com/s/articleView?id=sf.domain_name_overview.htm&type=5