The Hanuman Chalisa is a devotional hymn of forty verses (chaupais) in praise of Lord Hanuman, composed by Goswami Tulsidas.
What it speaks of
The verses praise Hanuman's strength, wisdom and devotion to Lord Rama, recall episodes from the Ramayana, and ask for courage and protection.
When people recite it
Many recite it daily, and especially on Tuesdays and Saturdays.