Namespaces and classes

Question

Right..!! I'm a guy with almost full fledged knowledge of C- language and I'm on my way to learn my C++ course . Btw I'm trying to learn C# and I'm totally confused regarding namespaces and classes: Things that bother me: 1. What is a class??.. P.S. I need it simple.. :P 2. Can I give any desired name to a class?? If so why?? 3. What is a namespace?? 4. How can I call a namespace (if I can)... Is it same as calling a user defined function from main in c-language??
5. One more thing.. I get confused of these "Public", "Static" and so on prefixes that are added to "Main". Please explain..
P.S. If I did ask any questions that are wrong in itself, please please do correct me.. Anxiously waiting..

Vulpes · Answer

Taking those questions in the same order:
1. A class is simply a blueprint for creating objects of a particular type.
Such objects are always stored on the heap and  a variable of the class type always contains a reference to where the object is stored (or null if it doesn't currently refer to an object), not the object itself.
2. A class name must be a valid identifier i.e. it can only include letters, numbers or underscores and must not begin with a number.
Although it's bad practice to use a reserved word (such as class, double, if etc) you can do so if you precede it with an @ sign. So this is valid:
class @class { }
3. A namespace is a way of organizing classes or other types and for resolving name clashes.
Suppose you import a library which contains a class called Foo and you also have a class of that name in your project. Then you can distinguish between the two Foos by prefixing them with their namespace.
4. You can't 'call' a namespace. It's not the same thing at all as a user defined function in the C language. The nearest that C# has to the latter is a static method of a static class.
5. The Main() method must be static but it doesn't matter whether it's public or not - the CLR will still be able to find and call it.
It needs to be static because, if it were an instance method, then it couldn't be the entry-point to the program - an instance constructor for its class would need to run first.