This is cumulative, doesn't have to be done all at once.
When you click the top channels button, it'll show you the top x number of channels. The really low channels (under 200 or so viewers) won't show up, so you'll have to go to the games section and click on random games (or one you want to watch) and see if someone's streaming that game that has less than 10 viewers (viewer count is denoted on the channel picture with a little person icon and a number).
If you have the Twitch app snapped you'll see the amount of viewers. Since this amount never changes unless you back out of the channel and start it again, it may count towards this achievement even if the viewer count goes above 10 if you started watching while there were less than 10 viewers.