1. We believe Allah (God) is very forgiving and as long as you believe in him you have a chance to go to heaven, but anyways us MUSLIMS to increase our chances we believe that we should pray, donate to the needy, believe in god and that mohammed is one of his prophets ( BY THE WAY Common misconception, we believe that there was jesus, moses all of the other prophets, we just don't believe that jesus was gods son), also to fast during Ramadan, To do the hajj (pilgrimage, i will go into detail why). These we call are the 5 main pillars of islam.
2. I suppose you mean to visit Mecca, and the kaaba, and to complete the Hajj atleast once in their life time, its supposed to show how strong muslims are, and how we completely submit to god, and will do anything for him.
" The Hajj is associated with the life of Islamic prophet Muhammad from the 7th century, but the ritual of pilgrimage to Mecca is considered by Muslims to stretch back thousands of years to the time of Ibrahim (Abraham). Pilgrims join processions of hundreds of thousands of people, who simultaneously converge on Mecca for the week of the Hajj, and perform a series of rituals: Each person walks counter-clockwise seven times about the Ka'bah, the cube-shaped building which acts as the Muslim direction of prayer; kisses the Black Stone in the corner of the Kaaba; runs back and forth between the hills of Al-Safa and Al-Marwah; drinks from the Zamzam Well; goes to the plains of Mount Arafat to stand in vigil; and throws stones in a ritual Stoning of the Devil. The pilgrims then shave their heads, perform a ritual of animal sacrifice, and celebrate the three day global festival of Eid al-Adha."
3. Through the angel gabriel, mohammed(sas) was believed to restore god's original message which we believe has been distorted, due to people before mohammed (sas) changing and tampering with the earlier texts. Anyways we believe him to be kind of the restorer , we believe that God sent the angel Gabriel to give to mohammed (sas) the messages that are now in the Qur'aan. Christains don't believe in mohammad(sas), inspite of the fact that Jesus himself said that "There will be one last messenger who will come after me, his name is Ahmed (another way of saying Mohammed (sas)"
I hope i have helped you.