PHP allows files to be uploaded to servers. The <form> tag must have the enctype attribute set to "multipart/form-data" for file uploads. The <input> tag type should be "file" which adds a browse button. Cookies are used to identify users and are stored on the user's computer. Sessions store information on the server and are available across pages, but are temporary. Functions like setcookie() create cookies, session_start() begins a session, and error_log() sends errors to logs. parse_ini_file() parses configuration files into arrays.