Du'a (prayer or supplication) is worship
Allah loves to be asked, and He encourages us to make Du'a in all things. Allah is angry with the one who does not ask of Him and He encourages His slaves to pray of Him.
Allah says (interpretation of the meaning):
"And your Lord said: "Invoke Me [i.e. believe in My Oneness (Islamic Monotheism) and ask Me for anything] I will respond to your (invocation)." [Ghafir 40:60]
Du'a is very important in Islam , so much so that the Prophet (peace and blessings of Allah be upon him) said: "Du'a is worship." (Narrated by al-Tirmidhi, 3372; Abu Dawud, 1479; Ibn Majah, 3828; classed as sahih by al-Albani in Sahih al-Tirmidhi, 2590)
This book shows you that way to make Du'a such that it will be accepted by Allah. It also contains the must know supplications that you should keep saying throughout the day for success in this life and the Hereafter.