After the Mash/Lauter Tun (MLT) is used to soak (or 'mash') the grain in hot water, the grains are rinsed (or 'sparged') with water and the resulting malt sugar solution is pumped to the Boil Kettle (BK) where it is boiled with hops for seasoning.
Before hops are added this malt sugar solution is called 'sweet wort'. After it is simply called 'wort'. It's not considered 'beer' until later when the yeast has been added and has had a chance to convert the sugars into alcohol.
After the grains are soaked (mashed) they are rinsed and the resulting sweet wort is pumped to the Boil Kettle.
Building the Boil Kettle is the most straightforward of all three kettles. The heating element should already have been added to your Boil Kettle as per our Heating Elements article. The instructions below will now show you how to install a Hop Stopper filter screen, a temperature probe, and a quick disconnect to the existing ball valve so that hoses can be connected to the kettle output.