How do you use Alpha channels on B&W images to create semi & full transparency?

Hello!

I used to use alpha channels in the older versions of Photoshop to convert any white to transparency & any black to full opacity.

The alpha channel would also create varying degrees of transparency & opacity based on how white or black (grey, light grey etc...) any part of a black & white image was.

I've been searching high and low to try to find some help but I'm just at a loss.

Any help would be appreciated! I create tattoos for second life and after a few years hiatus I'd like to get back into it but unfortunately I can no longer use the old technique I had saved in an action. I lost the action I created but even when I try to reproduce the old steps it just doesn't work anymore.

Thanks in advance!