Good morning
To go from kings cross to Buckingham palace you have to take the underground.
You will take the Victoria line ( the blue line) at kings cross until green park ( blue line ) there is only 4 stops. It won’t even take you 10 minutes. Underground is very quick.
when you arrive at green park station you will have to walk through green park To arrive at buckingham palace.
its not long , about 10 minutes walk.
Have a nice day
