Hello, I am developing a site using PHP. I want to know how to update a web page without reloading it. If possible, provide an example.
I don't have a specific example for you, but pretty much any AJAX/PHP tutorial out there on the interweb should show you some examples. You could also look into using JQuery, which includes AJAX methods.
That's such a broad request that it's impossible to provide an example; "update a webpage" could mean anything.
Just Google "ajax examples php" and I'm sure you'll find more than enough.
As others have said, this is such a broad question that it's hard to answer. Read a few tutorials and try to apply them to your code.