Wikipedia has a fine description of the rules for Conway's cellular automaton, Life, also described in 1970 in Scientific American. Briefly, it is a rectangular grid of ones and zeros, where the cells in each new generation are based on how crowded the neighborhood was in the previous generation. The attached JSL demonstrates a glider gun. There are much faster algorithms, and there are simpler ones too; this one falls in the middle.
Gosper's glider gun
Here's a 4K video made by adding some coloring rules and tossing in patterns randomly chosen from lifep.zip. Watch it if you are having trouble falling asleep and have bandwidth to burn, it's 40+ minutes. There is a major plot twist about three minutes from the end.