This blog post explains the difference between these different apps. 

Different Types of Apps

1. Canvas App is a low-code platform for building rich business applications.
2. Model-driven app design is an approach that focuses on adding components such as forms, views, charts, and dashboards to tables using an app designer tool.
3. Power Pages is low code / Pro Code software as a service (SaaS) platform for creating, hosting, and administering modern external-facing business websites. We can say an advanced version of Power Portal (Previous Version)

Difference between Canvas App vs Model-Driven App vs Power Pages (learntoilluminate.com)

Learn PowerApps directly in PowerApps with this interactive, hands-on material. This chapter covers galleries and data filtering, sorting and searching, in 10 tasks for you to complete.