Notice that a couple of other buttons have appeared next to the first Index View window. The second button, a filled square, is used to fill the Index subset (and thus to undo the effect of the empty button above it). The third button, an empty circle on a full background, does the Boolean "NOT" operation, inverting the contents of an Index subset.
On the next card in this Guided Tour, you can see the result of some further scrolling around in the same subset, defined by proximity to FREE or FREEDOM. I scrolled the first Index View to COMPUTER, which has only about 3% of its occurrences in the neighborhood of either FREE or FREEDOM (or both). I clicked on the word COMPUTER, and the Context View changed to show four occurrences of COMPUTER. Note the lines of dots ('. . . . . .') -- they indicate "deserts" in the subset, regions where 100 or more instances of COMPUTER were skipped because they weren't near FREE or FREEDOM.
Look over the next card, and then please continue the tour to see some more advanced features of Free Text.
