KTrotter

I am very new to Affinity Photo. In Photoshop, in an RGB document, the channels are RGB, Red, Green, and Blue. What is the equivalent of the "RGB channel" in Affinity Photo? I'm trying to do something in Affinity Photo that I've done a lot in Photoshop (Separate the shadows and highlights from an object and the object's color info) but I just cannot get it to work. I can provide the ink to the PS tutorial if necessary. Thanks for the help.