What is an Opportunity?
Opportunities display important details about the deals your teams are working on, like how much each the deal is worth, who you’re competing against, and what stage the deal is in. Opportunities also track all associated activities as they happen to close deals faster. With opportunities, you’ll never be out of the loop.

The Opportunity Management module maximizes the efficiency of your sales team by helping to manage and identify the best strategy for moving to close the deal, capitalize on sales potential with prospects and increase business from existing customers.

What does an Opportunity in MangoApps mean?
Users can sync their opportunities from different CRM packages including: Salesforce, SugarCRM and Siebel. Then, with everything at one place, collaborative opportunities are easy to find, give fast to access to updates and everyone can keep track of that opportunity.

Where can you configure CRM Integration?
Domain Admin could configure CRM provider from Admin portal.

Click on Modules from the left navigation and select CRM from the secondary navigation.

Or refer to this article:
How do I set up my CRM in MangoApps?

Users can sync opportunities from SugarCrm, Salesforce and Siebel into MangoApps. Just select an option from the drop-down menu and fill in the required details. Opportunites from your CRM will be synchronized to Mangoapps. You can start using opportunities from Mangoapps instead of logging in to another domain to use it.

For more details related to Salesforce opportunity configuration, you can refer following article:
How do I integrate Salesforce as my CRM in MangoApps?