Alert when Wm%R falls under -20

You need to add a time frame modifier in front of everything that will take one - the time frame modifiers are "daily", "weekly" and "monthly". For instance, for the indicator it would be

and [weekly Williams %R(14) < -20.0] // modify to suit your needs

If you have other requirements, like volume, those need to be modified, too, to be consistent. For instance,

and [weekly sma(10, weekly volume) > 1000000] // or whatever

You might also want to add something about past Williams readings being above -20, so,

and [2 weeks ago weekly Williams %R(14) > -20] // or something like that

Otherwise, you may get anything that is below -20 for any amount of time instead of something just arriving there.

You should be able to use a list.

On the alert workbench, find the drop down labelled "Your Chartlists".

Select the list you want and click "Add". You should get something like

and [favorites list is 99] // name of your list

Move this text to the top of your scan so it is the first line and edit out the "and", so it looks something like this:

[favorites list is 99] // name of your list
and [weekly williams %R(10) < -20.0]
and [1 week ago weekly williams %R(10) > -20.0]