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..