The Legend of Zelda: Breath of the Wild - Prologue Walkthrough
When you wake up, go to the pedestal and take the sheikah slate. This will open the nearby door.
Before you go, open the two stone chests. You'll find the old shirt and some well-worn trousers.
The next room has a door. Examine the pedestal to open the door.
Once you have all the items, climb the small ledge and head outside to start a cutscene.
You can talk to the old man, but it's not necessary. Just go down the slope past him to start the main quest.
As you go to the yellow marker, you'll see some ruins to your right. In the square ruins to the north, there's a treasure chest with Hylian trousers inside.
Follow the yellow marker and you'll find a pedestal hidden in some rocks. Study it to activate the great plateau tower.
You will be on top of a tall tower. To get down, run along the ledges. You might want to save your progress in case you make a mistake.
While you're down, a cutscene will trigger and you'll start your next main quest.
Go to the top of the nearby hill and talk to the old man there. He will point you towards your next objective.