To start, go to the Home Assistant Overview page, click on the three dots at the top right of the screen and select ‘Edit Dashboard’. Then click on the blue ‘+ Add Card’ icon at the bottom right and select a card to add.
You created an automatically generated dashboard - where you cannot add cards.
Guess this is a default option for beginners…
Create a new dashboard and select smth like “not automatically generated”.
As suggested you need to go into settings then dashboards, then in the bottom left add dashboard, new dash from scratch give it a name and let it be shown in side bar.
Then go to new dash edit and add cards from bottom left icon. Then spend the next 6 weeks tumbling down the rabbit hole which is dash creation. When you get it right it will be worth it.