what is the use of database.saveresult in salesforce?

Each element in the SaveResult array corresponds to the sObject array passed as the sObject[] parameter in the database method, that is, the first element in the SaveResult array matches the first element passed in the sObject array, the second element corresponds with the second element, and so on. If only one sObject is passed in, the SaveResults array contains a single element.

To know more you can go through this link- https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_dev_guide.htm