The .NET CLI is how you'll do .NET development outside of Visual Studio. If you've got a top of the line machine, you may not ever need to leave Visual Studio, but for the rest of us, it can be slow and a pain to use for small or quick projects.
For these times, you can use Visual Studio Code or the text editor of your choice. You can use the .NET CLI to create your solution, add projects, add references, add NuGet packages, build, and deploy your app.
Here's a video showing some quick examples.