Bob's got it right, that's a standard cereal mash, but indeed with little detail. Here's the full procedure. The unmalted adjuncts, along with 10% of the total malt, are mashed in at a standard water to grist ratio for a target temperature of 122°F (50° C.) At the same time, the remaining malt (called the main mash) is also mashed in, in the normal fashion, at 122°F (50°C) and held there for a protein rest. The cereal mash, meanwhile, is immediately raised to boiling and boiled for 10 minutes to fully gelatinize the starches (enzymes in the malt aid in liquefaction of the cereal mash, so you don't just make porridge.) The boiling cereal mash is then mixed into the main mash to bring the entire, combined mash up to conversion temperature (just like a decoction,) and from there, conversion, mash off and sparging proceed as for a normal step mash.
(If all that seems like a PITA, it is. That's why many brewers have long preferred flaked adjuncts, which are pre-gelatinized and can just go into the mash with the malt, over grits. If a recipe calls for grits and a cereal mash, you can just substitute flakes and do a regular infusion or step mash. If there's a large amount of adjunct, you'll still want to include a protein rest to ensure sufficient FAN for the yeast.)