Conceptually, when the foreground color is completely opaque, the resulting blended color will be the foreground color. If it is transparent, the blended color will be the color of the background. When the value of the alpha channel is $1$, the image is all there, if it is $0$, there is no image at all, otherwise it is only partially there. In other words, the alpha value goes from $0$ to $1$, where full transparency is $0$ and opaque is represented by $1$. Alpha blending models opacity.
Conceptually, when the foreground color is completely opaque, the resulting blended color will be the foreground color. If it is transparent, the blended color will be the color of the background. When the value of the alpha channel is $1$, the image is all there, if it is $0$, there is no image at all, otherwise it is only partially there. In other words, the alpha value goes from $0$ to $1$, where full transparency is $0$ and opaque is represented by $1$. Alpha blending models opacity.