I'm just learning C# so I don't know if I'm just messing up the setup or what, but I used dotnet to create a new project where I'm keeping ALL of my little test scripts. I'm using VS Code as my editor. I create a path variable for csc to compile.
I can compile a Hello World project no problem, but I'm working through this course online and the next part was to make a simple gradebook.
I have GradeMain.cs
namespace Grades
{
    public class GradesMain 
    {
        static void Main (string[] args) 
        {
            GradeBook book = new GradeBook();
            book.AddGrade(91);
        }
    }
}
And GradeBook.cs
using System.Collections.Generic;
namespace Grades
{
    public class GradeBook
    {        
        public void AddGrade (float grade) 
        {
            grades.Add(grade);
        }
        List<float> grades = new List<float>(); 
    }    
}
When I try to compile using csc I get the following error
error CS0246: The type or namespace name 'Grades' could not be found (are you missing a using directive or an assembly reference?)
My intellisense shows that my GradeBook has two references from GradeMain. I saw this post Referenced Project gets "lost" at Compile Time but since I'm not using visual studio I wasn't sure if it was related / how to check my dotnet client profile.