Spin down the Text layer properties, click the Add button and add Transparency.
Spin down the text animator properties and select By Word, then start setting keyframes.
If you want to automate the words appearing, you'll have to turn the audio track into an audio track with markers. You can do that with Premiere Pro or Adobe Audition. Adobe Premiere also has an automated subtitling feature. If your comp is longer than a sentence or a phrase, you'll be better off in Premiere Pro.
I have uploaded a sample project.