Overview
Nafl salah, like Sunnah salat, is not obligatory but has extra benefits on the person performing them.
General Nafl prayer
General Nafl salah can be prayed before or after any salah, or on its own at any time that prayer is allowed, just to gain extra blessings.
Ishraq prayer
Ishraq prayer begins ten to fifteen minutes after sunrise and consists of two Raka'ahs. Praying ishraq is considered to yield greater rewards than performing the lesser Jihad according to some traditions.
Duha prayer
Duha prayer begins after sunrise and ends at meridian, and is generally thought to include at least two raka'ahs, though in some traditions the number is four or even twelve. It is generally prayed when one-fourth of the day has passed. Performing this prayer is believed to be effective in seeking forgiveness for one's sins.
Tahiyat al-Masjid (Greeting of the Mosque)
Also called "masjidus salam", this is a highly recommended prayer consisting of two Raka'ahs and performed when first entering a mosque. It is considered to be a way of greeting the place of worship in order to draw nearer to Allah.
Khawf
The word "Khawf" means fear. Khawf is a type of prayer that is prayed during time of fear. This prayer was performed by Prophet Muhammad in the Battle of Uhud. It is considered to be a substitute for normal prayers while on a battlefield.
Journey prayer
When a person is about to travel, and also when they return from traveling, it is considered beneficial to pray two Raka'ahs in a mosque.