Skeleton of declaring class is:

<>:Required

[]:Optional

[private/public/protected/internal] class <Desired Class Name> [:[Inherited class][,][[Interface Name 1],[Interface Name 2],...]
{
    //Your code
}

Don't worry if you can't understand whole syntax,We'll be get familiar with all part of that.for first example consider following class:

class MyClass
{
    int i = 100;
    public void getMyValue()
    {
        Console.WriteLine(this.i);//Will print number 100 in output
    }
}

in this class we create variable i with int type and with default private Access Modifiers and getMyValue() method with public access modifiers.