A photosite or host site is where you upload your pics to your gallery for storage. You can then move them to a forum post via the image link.
Check out www.photobucket.com and register for a free gallery. They will notify you of the address, Make a folder (IMAGES) and copy address.
To upload click Browse, at your gallery, and your computer will open showing pics, click on image and then click open at the bottom of the page. You will automatically be directed back to photobucket; click Submit and pic will upload to the gallery.
To transfer to forum, (copy/paste) click the URL TAG (1st/top) Tag will turn blue, right click and choose copy, come to forum, post topic/reply and click on [img] on above task bar, place cursor(*) between the link symbols (]*[) and paste, then submit post...[OK]