how to use og meta tag for facebook share

The tags look something like this

<meta property="og:title" content="TITLE" />

<meta property="og:url" content="URL" />

<meta property="og:image" content="IMAGE_URL" />

<meta property="og:description" content="DESCRIPTION" />

How to clear Facebook's image cache

The way to "force" facebook to clear their cache for a specific url is to use the Debugger tool.

Debugger tool url : https://developers.facebook.com/tools/debug