Start here. This is the direct spoken answer to practice first.
Why this question matters
GitHub Actions and Azure DevOps can both deliver a .NET product well. The useful comparison is how each fits the repository, permissions, environments, governance, and operating habits of the team.
Both GitHub Actions and Azure DevOps can build, test, package, and deploy .NET applications. GitHub Actions is convenient when the code is already in GitHub and the team wants workflows close to the repository. Azure DevOps can be strong for organizations already using Azure Boards, Releases, approvals, and enterprise governance. I would choose based on the ecosystem, security model, team familiarity, and deployment needs.