Steps to draw the Lorenz curve
Step 1: put the persons in order from the lowest to the highest income
Step 2: divide the people in equal group (eg 5 groups) from lowest to highest income
Step 3: calculate for each group the percentual part of the group of persons compared to the total group (eg 5 groups means every group of persons is equal to 20%) and how much their income is compared to the total income
Step 4: add all the percentage groups together
Step 5: draw the Lorenz curve.