If there is a rail hold onto it with one hand.
Place one crutch in the other hand.
If there is no rail you can use 2 crutches.
Walking up stairs:
Stand at the bottom of the stairs.
Bring your affected leg behind you so that you don't bump your toes on the way up.
Push through the crutch and rail and hop your unaffected leg onto the first step.
Then bring the crutch up to the same step.
Repeat the pattern until you get to the top.
Walking downstairs:
Stand at the top of the stairs.
Keep your affected leg forwards out of the way so that you don't bump it on the way down.
Take your crutch down to the first step.
Push through the crutch and rail and hop with your unaffected leg down onto the first step.
Repeat this pattern until you get to the bottom.