If you're referring to brew in a bag, the water is heated to strike temps (with a full volume mash a couple of degrees above desire mash temp) taken off the heat, the bag is the put in to line the pot, grains added, mashed, grain bag removed the brought to a boil and boiled for 60-90 mins.
Generally when people have a false bottom, its on a mash tun. Brewing in a bag is an alternative to having a dedicated mash tun. You can have a fb on a boiler, but a hop filter (or just some copper with a few holes drilled into it) is normally used instead.