The word “instance” refers to a single, independent execution of the Home Assistant software on a server. So, your Home Assistant and all the integrations it is using, running on your server, is your “instance” of Home Assistant.
If you go to the Dashboard documents, in the left-hand sidebar menu you will find links to all the documentation for core card types.
But how do I add a larger element like a webcam video or a big weather dashboard to my “homepage” or “main dashboard” ?
All i am able to to is adding these small buttons - showing just one value or parameter of my webcam or my weather plugin