I can't find the `Alpha' slider

I have the 1.3 hardcover manual which refers to the Alpha slider. I have Blender version 1.42 which does not appear to have an alpha slider anywhere in the materials section. There are buttons for ZTransp' andRay Transp’ but no Alpha' slider. I tried searching the forum for keywords like transparency and Alpha slider but the threads I found still left me clueless. I've also played endlessly with the buttons; trying any combination that looked related. No joy. If I map the texture toAlpha’ I just get a plain gray surface. If I map to color I get the texture image showing up on my plane or cube.

How do I get a cloud texture to produce a pattern of transparency on a simple plane?

It’s just labelled “A:” beside the DYN button