Find the general solution for the problem y'' + 2y' + y= e^-t.. solve with initial conditions y(0)=0, y'(0)=1

i get the eigen values are both -1, which is e^-t.. that is the term on the right side of the original equation. im completely lost at this step.. really appreciate it if someone could help me out with this (sorry for the vague title, wasn't really sure what to call it)