Make words appear on screen by popping up as the speaker says them with this technique in Final Cut Pro X.
I haven't found a great method for making words appear exactly when they are spoken, but this method works pretty well for me.
As soon as I finished editing this video, I thought "it would make even more sense to play the clip, pressing M when each word starts. Then just line up the keyframes with the marks." Bonus if you read descriptions.
I find this method quicker than the method Emilio Takas uses in his video Popup Text Effect in Final Cut Pro X. Instead I use a mask and keyframes to animate the text.
Be sure to use two keyframes for each word. One with the previous location and the next frame should have the new location of the mask. If you don't do this, the mask will morph from the last keyframe leading to a crappy look :-(
Hopefully this helps you show text on screen while talking - editing with FCPX.