JEE Main will be conducted twice a year one in the Month of January and Second in the month of April. 

The scores of Attempt 1 will be converted into percentile scores, Percentile Indicates the percentage of Students who scored less than you. Similarly, Attempt2 will be converted into percentile scores, Now those who appeared in Both, Attempt with Higher percentile scores will be considered, And based upon that All India Ranks will be calculated.