Class

class TestClass
{
    // Methods, properties, fields, events, delegates
    // and nested classes go here.
}

• Classes are declared using the keyword class.
• Classes that you declare directly within a namespace, not nested within other classes, can be either public or internal. Classes are internal by default.
• Class members, including nested classes, can be public, protected internal, protected, internal, private, or private protected. Members are private by default.

class ClassA { }
class DerivedClass: BaseClass { }

class ImplClass: IFace1, IFace2 { }
class ImplDerivedClass: BaseClass, IFace1 { }

Only single inheritance is allowed in C#.

A class can inherit implementation from one base class only.