(x+3) (x-1)
Take the first term from the first bracket that is x and times it by the second bracket. x(x-1)
now take the second term from the first bracket that is +3 and times it by the second bracket. +3(x-1)
so you have
x(x−1)+3(x−1)=x2−1x+3x−3=x2+2x−3