OK so they are just breaking down the equation and showing every sing step. The far left side [ (a+b)^2 ] answers at the bottom are going to be 2a and then 0. The middle part [ (c)^2 ] answers at the bottom are going to be 0 and then a^2 + b^2. The right side of the equation is going to be 4ab/2 then 2ab then 2ab again then 2ab+c^2 then 2ab-2ab+c^2