There are three main types of Power Apps; Canvas, Model-driven, and Portals
Integrate with data from a near limitless number of Microsoft and third-party data sources and build a pixel-perfect interface using buttons, lists, text inputs and more for a tailored user experience. Apps can then be deployed for use on mobile or tablet devices, in a standard web client, or even embedded in Teams, Sharepoint, or Power BI dashboards.
Canvas app design provides the following benefits:
With Model-driven apps, you can implement business process flows to ensure consistency and provide structure to processes by defining stages and actions for users to progress through.
Model-driven apps provide the following benefits:
Power Apps Portals is the newest type and focused more on website design. In simple terms, what a Canvas app is to app design, a Portal is to web design.
It's an easier way for people to create external-facing websites using a straightforward studio and expose data to customers and vendors (and those people can be guests, they don't have to login). Also, if you want to get a bit techy, you can even mess around with the CSS!
Portals share a lot of the framework of model-driven apps in that both are built around Dataverse, and have access to the pool of Dataverse components (Views, Forms etc) as well as the data stored within.