Dynamically adding contents to ContentPlaceHolder

hi, Recently delved into asp.net v2. I'm attempting to implement masterpage where I need to dynamically create contents for a particular ContentPlaceHolder on a page. How does one do that? I know that ContentPlaceHolders are publicly exposed. I think I would need to write public methods on MasterPage to expose the ContentPlaceHolder. Any help out there would be greatly appreciated. Thanks.