I saw this while cycling through the graffiti tunnel on Sunday.
'The world is your oyster' is an expression that means - you can go anywhere in the world and do anything that you like'. (I don't know why - perhaps you could find out!)
We're staying at home so the world isn't our 'oyster' at the moment!
Have a look at this Bitesize page though for some learning and games about our big wide world. We may not be able to go very far at the moment, but this won't be forever so take the time to learn a bit about our world from the comfort of home!