The last of the 5 pillars of Islam is to perform a pilgrimage, or Hajj, to the Kaaba (Mecca, Saudi Arabia) at least once in a Muslim’s lifetime. This is a difficult and arduous feat, but the Muslim who performs Hajj correctly will receive unlimited rewards.
The Hajj is especially important in bringing Muslims together. Muslims are spread out all over the world. Performing the Hajj pilgrimage helps to bring the global Muslim community together in a unique way. Only those Muslims who are financially and physically able are required to perform the Hajj.
But for the one who does it, conducts themselves in the appropriate manner, and performs all of the required rituals as taught by Prophet Mohammad, they will have all of their previous sins wiped clean. Inshallah.