1. Blending modes need two or more layers for any effect to work — you need at least two layers to “blend” together.
2. A layer with a blending mode specified will “blend” with all other colors from layers underneath it. We call those original layer colors the “base colors.” The colors on the top layer (with the blending mode selected) is called the “blend colors.” The result — what you see as a result of the “blending” — is called the “result color.”