How to use X-sheets:
1.
Look at an X-sheet that's filled out as an example. Animators use them as a guide for when dialogue phonemes are hit, how long they're held, and what phoneme shape is used. You can also make notes about particularly strong phonemes, or which point is the most emphasized in the dialogue. Animators often put doodles and notes about acting in here too.
2. Find a clean sheet that you like, or make your own in Word/Excel. I prefer ones that have marks every second (24 frames).
3. Put the sound clip you want to use into a program that can scrub frame-by-frame, such as Flash, After Effects, Vegas Video. Make sure it's demarcating at the proper frame rate. Go through frame-by-frame, listen to it, and mark your exposure sheet accordingly.
Now you don't need the sound clip in front of you to sync your animation. Follow your X-sheet and if you've done it correctly, your dialogue will be synced when you scan it in.