4 answers
What application did you install? Was it from the AppExchange? Why are they asking you to "review the database structure"? Was there an error?
I'm only guessing here without having more details, but I'm assuming they are referring to the data model of your org. The easiest way to view this is using the schema builder in Salesforce. Just go to setup --> search for Schema Builder. You can select and deselect objects on the left side to make it more easily understandable. This essentially acts as Salesforce's entity relationship diagram.
Resource
Data Modeling Trailhead (https://trailhead.salesforce.com/en/content/learn/modules/data_modeling" target="_blank)