What is SLR Camera and how it's differs from usual cameras ?

I don't understand the title of this thread - ?

Single-lens reflex camera - Wikipedia, the free encyclopedia

I changed the title of your thread and moved it to the appropriate forum (from Entertainers). A key to getting help on a site like this is to place your question in the proper forum and use a title that describes your question.

The link in your first response should help you.