To steel yourself means to make yourself strong and ready to face something difficult or unpleasant.
When you steel yourself, you are getting ready to be very brave and strong.
Examples:
She steeled herself before going into the haunted house.
He steeled himself for the big test.
They steeled themselves for the long journey ahead.
I steeled myself before trying the really sour candy.
Before the race, she steeled herself to run as fast as she could.
He steeled himself and went to talk to the scary teacher.