Welcome to the HP Support forums. I understand that you would like to learn how to setup HP's ePrint feature for your Officejet 8500.
If you have an Officejet Pro 8500 A909 series printer then it predates the ePrint feature. If you have the wireless version of the printer (A909g) you may be able to use the HP ePrint app to print from a mobile device connected to the same wireless network as the printer. I've included HP ePrint Mobile app FAQ document for reference.
If you have an Officejet Pro 8500a A910 series printer you should have the ePrint icon in the upper left hand corner on the front panel of the printer. The icon looks like this
Welcome to the HP Support forums. I understand that you would like to learn how to setup the ePrint feature of your Photosmart 7520 printer.
First the printer needs to be connected to your wireless network before we can enable the web services to get your printer claim code. You can easily do this from the front panel of the printer. The instructions can be found in your User Guide on page 48 in the section titled "To connect the printer with the Wireless Setup Wizard".
Now that the printer is setup on your wireless network we need to enable the web services. You should be prompted to accept the terms of service when you first enable web services. If a summary screen is displayed with an email address that you didn't create, please choose settings and disable the web services. That will allow us to start fresh. Once you have enabled/re-enabled the web services an information sheet should print out with the claim code.