Bind a variable in ASP tag.

Hi all,
    In my application i need to bind a variable which i m having in my code behind C# file, to a Hyperlink's NavigateURL property.
NavigateURL="some path/file.aspx?id={C# variable}"  How to do that??
And what does this '<% %>' mean??
#,$,= can be used within those tags. But what is their individual use??
...