Power app is one of the low code platforms. It is Microsoft service for building apps that can run on mobile and web platforms. The main aspect we must understand while creating an application with power app is we have two options for creating an app. One is canvas and other is model driven.
Canvas app has been in existence for a longer period of time than model driven app.With canvas app we can prepare an app with WYSIWYG design tools so we have a lot of control over user experience of the app. The app can be configured as per requirement of a user. It also can be connected to different data sources using connections like: CDS(Common Data Service), SharePoint, Onedrive, etc. We also can use formula code which resembles one with excel formula.
Before understanding Model Driven app we have to get an idea of Common Data Service. It is a service built over Common Data Model that allows users to build, manage, store apps and their data. Common Data Model is a secure business database implemented by Microsoft as a service for CDS. It has entities like Accounts, Contacts, Opportunities, Products, etc. These entities contains fields as addresses, phone numbers, etc. We can also add entities on our own which can be used across apps using Common Data Service. Powerapps and Microsoft Flow mostly utilizes this service. CDS is a main factor responsible for cross-platform integration.
Model driven app uses entities, data structures for preparing an app. It can be used as standalone or as the backend to canvas app. It is capable of generating data models.
The layout for model-driven apps is mostly defined . When we define a model driven app we are making a Dynamic 365 instance where everything revolves around model, entities and driven by business processes.
Here is a simple figure I found on the web that depicts difference between canvas and model driven app.
After understanding the type of app we are going to use we have to be familiar with the environment. It is a space to store, manage and share your organization business data, apps and flows. It also serves as containers to separate app that may have different roles, requirements and users.For preparing an app with power app we must also set the environment. Some environment might not have authorization to create new entities so we might create an environment. Power app provides us to create an environment for 30 days trial period where we can create apps. But for using them for more than that time we must shift environment to production by buying environment.
We also must be familiar with the concept of connections to connect data with our app. The connectors are mainly required for canvas app to create a connection. PowerApps has connectors for many popular services and on-premises data sources, including SharePoint, SQL Server, Office 365, Salesforce, and Twitter. It also can establish connection with apps like google docs.A connector may provide tables of data or actions. Some connectors provide only tables, some provide only actions, and some provide both. Also your connector may be either a standard or custom connector.
Powerapp also consist of flow. It is same as Microsoft Flow which is a service that helps us to create automated workflows between apps and services to synchronize files, get notifications, collect data, etc. Here, we can include the steps in which an app gets request or response from another flow and provide content accordingly which may be either static or dynamic. The flows can be added as actions.
We also can include some function values for buttons, labels, gallery, etc. The function can be added on any of the options provided like OnSelect, Visible, Items, etc.
Since, Canvas App is common in powerapp let us build a small canvas powerapp.
To build a shopping cart app you can go through this tutorial:
https://www.youtube.com/watch?v=aOcQIMvdWW4&
To know about sharepoint list go through this tutorial:
https://www.youtube.com/watch?v=OiboJXAWZm8
For pop up you can go through this tutorial:
https://www.youtube.com/watch?v=IvapIsBbM-U&
For basic model driven app you can go through following tutorial:
https://www.youtube.com/watch?v=TUxEQKYv0oU