Step 3: Hold a finger on the screen
Use your other hand, and maintain contact with the screen. Then...
Step 4: Swipe to your second filter
There are currently three "classes" of filter: middle, perimeter, and whole-screen. You'll notice that if your first filter is from the former group, you'll only be able to access the latter groups for filter #2. (Otherwise, they'd fill the same space, and look like butt.)
Step 5: Place your finger on filter #2, and swipe
BOOM. If you did it right, filter #3 has arrived. Now you've got a filter from all three classes. Nice work!
Bonus: FIVE filters (on videos only)
On videos, you'll have a fourth class of filters available: the ones that manipulate the speed and direction of the video. Repeating the same process, you should be able to apply: one color, one middle, one perimeter, slo-mo/fast-forward, AND reverse. Why? Mostly just because you can.