If you're making an attempt to select a file for upload selenium 2 supports HTML file inputs.
For example:
HTML
<input type="file" id="upload_here" />
Selenium Code
IWebElement element = driver.FindElement(By.Id("upload_here"));
element.SendKeys("C:\\Some_Folder\\MyFile.txt");
Basically you "type" (with SendKeys) the full file path to the file input element. Selenium handles the file selection dialog for you. However, if you would like to manipulate an arbitrary file selection dialog, you've got to travel outside of selenium.
If you are interested to learn Selenium on a much deeper level and want to become a professional in the testing domain, check out Intellipaat’s Selenium automation course!