Explanation
Expected revenue is calculated as Amount x Probability. If the expected revenue field displays incorrect values, it means that the probability associated with the stage is not accurate. The administrator should change the probability to reflect the actual likelihood of closing the opportunity at that stage. References:
https://help.salesforce.com/s/articleView?id=sf.forecasts3_expected_revenue.htm&type=5

Explanation
Web-to-Case allows you to create cases from a form on your website.
References: https://help.salesforce.com/s/articleView?id=sf.customizesupport_web_to_case.htm&type=5

Explanation
To create a many-to-many relationship between two existing custom objects, the administrator needs to create a junction object that has two master-detail relationships, one to each of the custom objects. This will allow each record of one object to be linked to multiple records from another object and vice versa. References:
https://help.salesforce.com/s/articleView?id=sf.relationships_manytomany.htm&type=5