et. al. = et alia = "and others". "If you visit the DC forum, you'll always run into RaySun2Be, ViRGE, Kilowatt, MechBgon, et. al."
i.e. = id est = "that is" (or "in other words"😉. Used when you are rephrasing a statement in different terms or as a way of explaining the statement. "That thread was full of name-calling, nasty, mean posts - i.e., a flame war."
e.g. = exempli gratia = "for example". Used when you are citing a specific example of a statement. "Many times you'll see the same topics over and over in Off-Topic, e.g., 'what are the different levels of membership?'."