I haven't used 'tell', but the 'ask' works like this below (unfortunately 'ask' isn't explained that well in how exactly it works ~ it took me awhile to figure it out too), if you don't mind code, it does show the concept well:
(if you do a lowercase 'ask', then it'll be a popup menu)
(if you do a uppercase 'Ask', then it'll be "in-line" ~ in the big text box as a hyperlink)
ask ("your message") {
// if you choose 'yes', then it sets: result = true
// if you chose 'no', then it sets: result = false
if (result = true) {
// script1
} else if (result = false) {
// script 2
}
}
hopefully you can figure this out in the GUI~Editor, if you don't know how to work with code yet.