If there is a rail, hold onto it with one hand.
Give your spare crutch to a grown up, or you may be asked to hold it.
If there is no rail, you can use 2 crutches.
Walking up stairs:
Stand at the bottom of the stairs.
Push through the crutch and rail and step your unaffected leg on to the first step.
Then bring your affected leg onto the same step.
Finally, lift 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.
Take your crutch down to the first step.
Step you affect leg down to the same step.
Finally, bring your unaffected leg down onto the same step.
Repeat this pattern until you get to the bottom.