Getting the user declared classes with reflection

I'm trying to access all the user declared classes in my project. My goal is calling functions of the classes that i access. I have made a research about it like 2 3 days , but i couldn't find any solutions.

I have tried to get types from assembly but it gave me so complicated results. Here is what i tried :

Assembly assembly = AppDomain.CurrentDomain.GetAssemblies();
Type[] types = assembly.GetTypes();

int i;
for ( i = 0 ; i < types.Length ; i++ )
{
    Console.WriteLine( types[ i ].Name );
}

Quick Example - If any other programmer that works on project creates a class called "Hello.cs" , i need to get that class and call the required function inside of it.

I'm stuck with the "getting user/programmer declared classes" part , any help is great.