To identify why a user is unable to log in to Salesforce, the administrator should review the login history for the user. The login history shows the date and time of each login attempt, the source IP address, the browser and platform used, the login type (such as username and password or single sign-on), and the status (such as success or failure). The login history can help troubleshoot common login issues such as incorrect username or password, invalid security token, IP restrictions, or login hours violations. Checking the attempted logins by running the setup audit trail, pulling the password history, or resetting the security token for the profile will not help identify why a user is unable to log in. Reference: https://help.salesforce.com/s/articleView?id=sf.monitoring_login_history.htm&type=5

The User Licenses related list in Company Information shows the types of licenses that have been purchased for an org and how many are available or used. It also shows the expiration date of each license type if applicable. This information can help administrators plan for license purchases and manage user access. Searching for license types in setup does not show how many licenses have been purchased or how many are available or used. User Management settings in setup does not show license information either, but rather settings related to user login, session, identity, etc. Usage-based entitlement related list in company information shows information about usage-based licenses such as API requests or sandboxes, but not user licenses. Reference: https://help.salesforce.com/s/articleView?id=sf.users_understanding_license_types.htm&type=5

A Trailhead Playground is a free, online learning environment that allows you to try out Salesforce features and apps. You can use a Trailhead Playground to test out an app from the AppExchange before you install it in your production org.
A sandbox is a copy of your production org that you can use to test changes and new features. You can install an app from the AppExchange in a sandbox to see how it works in your environment.
Testing an app in a production org is not recommended, as it could affect your live data. Checking edition compatibility is important, but it is not a way to try out an app.

Permissions and tab visibility are two options that administrators can adjust to fully restrict access to records for certain users or profiles. Permissions determine what users can do with records, such as create, read, edit, delete, view all, or modify all. Tab visibility determines whether users can see a specific object tab in their app launcher or navigation bar. By setting permissions and tab visibility to none or hidden for deal records for service users or profiles, administrators can prevent them from accessing deal records via search or other methods. Reference: https://help.salesforce.com/s/articleView?id=sf.users_profiles_permissions.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.customize_tabs.htm&type=5

Get Records is a flow element that allows you to retrieve one or more records from an object that meet certain conditions and store them in a collection variable or a record variable for use later in the flow. You can also choose which fields from those records you want to store in variables. Reference: https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_data_getrecords.htm&type=5