There are numerous examples at Wolfram Demonstrations project, even some by Stephen Wolfram:
So, download code and study them. Here is one version out of many. Rule:
GameOfLife = {224, {2, {{2, 2, 2}, {2, 1, 2}, {2, 2, 2}}}, {1, 1}};
Puffer initial state:
Puffer =
{{1,4},{2,5},{3,1},{3,5},{4,2},{4,3},{4,4},{4,5},
{8,1},{9,2},{9,3},{10,3},{11,3},{12,2},{15,1},{15,4},
{16,5},{17,1},{17,5},{18,2},{18,3},{18,4},{18,5}};
Precompute 100o steps of evolution outside animating module:
evo = N@CellularAutomaton[GameOfLife, {SparseArray[Puffer -> 1], 0}, 1000];
Animate showing trails of past generations:
Manipulate[
ArrayPlot[Mean@evo[[t ;; t + 200]], ImageSize -> 800, Frame -> False,
ColorFunction -> "TemperatureMap", PlotRangePadding -> 0],
{{t, 1, "steps"}, 1, 800, 1, Animator, AnimationRate -> 60,
AnimationRunning -> False}, FrameMargins -> 0]