Line them up forget about the decimal until the end after your done once you get the answer add the decimal by like umm let's see if you have 2.5*2.5 you would like add the decimal places one each for each number there there is one number after the decimal so like add the places the decimal was moved for each number and then add the decimal places together that why 2.5*2.5=6.25 you see? Do you understand what I'm saying? If not let me know
Hope this helps have a nice day!