The superstructure of Islam is raised on five (pillars) : testifying that there is no God (none truly to be worshipped) but Allah, and that Mohammad is the messenger of Allah, performing the prayer, paying the Zakah (poor-due), fasting the month of Ramadan, and performing Hajj.

http://www.ediscoverislam.com/Why-Religion-of-Islam/Convert-to-Islam/how-to-become-muslim-convert-islam