You must hav the webpages on ur computer, right? Now right clik on index.html (assuming that u wanna put the ad on ur homepage) and open the file with notepad.
now paste the code where u want to --must be somewhere between the body tags i.e. somewhere between <body> and </body> tags. (if u r not sure where u r to paste, experiment a bit, see where the ads show up on pasting the code where). Its that simple. do it urself. U wont need anyone's help.
If u hav uploaded ur pages once, u ll be able to it again. U can use cute ftp pro to upload.