File.Create(string) returns an instance of the FileStream class. You can call the Stream.Close() method on this object in order to close it and release resources that it's using:
var myFile = File.Create(myPath);
myFile.Close();
However, since FileStream implements IDisposable, you can take advantage of the using statement (generally the preferred way of handling a situation like this). This will ensure that the stream is closed and disposed of properly when you're done with it:
using (var myFile = File.Create(myPath))
{
// interact with myFile here, it will be disposed automatically
}