mkdir MyApp && cd MyApp
dotnet new sln -n MyApp && dotnet new web -n Api
dotnet sln add ./Api/Api.csproj && dotnet run --project Api
Many devs would want more features out of the box so they'd replace "web" in the "dotnet new" command accordingly (use "dotnet new list" to see the options, eg mvc, grpc, or react). But this is the minimalist option just to 'get something running'.
Edit: For background, new sln creates a new DotNet Solution and new web creates a new (minimal) C# web Project. Then sln add tells the new solution that the new project is part of it.