Introduction to GitHub
GitHub is not a part of the Azure DevOps product, but it is a product that is also owned by Microsoft. Before Microsoft purchased GitHub in 2018, it was a commercial company that implemented the Git technology and provided (free) remote Git repositories. Many people (still up to today) confuse the term Git with GitHub.
GitHub is just a commercial implementation of the Git technology, just like Microsoft did within Team Foundation Server and later Azure DevOps, or even other products/websites like Bitbucket, GitLab, and so on. GitHub has become well known because of its usage within the open source world. Many open source projects are hosted within GitHub.
There is a free version that you can use, but there are also subscriptions available for GitHub. Before Microsoft acquired GitHub, you could only host public repositories for free. This makes sense with open source products, but if you wanted to create private repositories as well, you needed a paid subscription. Microsoft changed that in 2019 and now you can host an unlimited number of public and private repositories for free. This free tier also includes Actions minutes, which you can compare to Azure Pipelines build minutes, and some Packages storage capacity.
There are still Team and Enterprise subscriptions available. They include more storage space and action minutes, and some other extra functionality.
You can find more information about GitHub pricing on the Pricing - Plans for all developers page.
The GitHub product is also constantly evolving. With the addition of action minutes, you can set up CI/CD pipelines, there is support for project management, packages, and so on. Much of the functionality that Azure DevOps offers is also available within GitHub.
It can be a good thing to compare the two products and see which one fits your needs the best. In this learning path, we'll only discuss the Azure DevOps product.