The info on this page is for OED version 1.0.0. See "Help versions" menu at top of page for other versions.
OED provides popup help (tooltips) within the web browser to help users.
Anywhere you see the icon, you can click to get a popup to see help on what is near the icon. This is shown in the next figure where the icon is highlighted with a blue box. The icon has been clicked and the help tooltip popup is shown for "Units". As is common, there is a brief description about the item and a link for further information in the help pages.
Normally only one popup is allowed but a few can be shown simultaneously.
There are help files for each version of OED. The version is shown in the footer at the bottom of each web page. When you click on a help link it will take you to the help for the version of OED that you are running. You can look at the help for other versions by using the "Help versions" dropdown menu at the top of all help pages. If the help page did not exist in a previous version that you try to go to then you get an error page.