Power Apps lets you build custom business applications quickly, without a full custom-development project. There are two main types: canvas apps, which give you pixel-level control over the layout and connect to hundreds of data sources, and model-driven apps, which are generated from your data model in Dataverse and are well suited to complex, data-heavy business processes such as case management or CRM-style applications.
If a team is running a business process from spreadsheets, email or a legacy Access database, that's usually a strong signal a Power App would remove manual effort and give you better data quality and reporting. We'll assess your process and tell you honestly whether Power Apps is the right fit, or whether a different part of the Power Platform, or a fuller Dynamics 365 CE implementation, would serve you better.