Okay, here it is (this was for Logic 9, but the process is the same in LPX):
Create a Marker for, let's say, the first line of the song, create it ± one bar
before the line actually starts. Set the Playhead where you want the marker, hit the key command for Create Marker
Now hit the command to open the separate *Marker Text* window.
Click on the Aa (LPX) button
- now you can enter the text.
If you click on the font you can format the (selected/highlighted!) text.
Repeat this process for every line (or you can do it with blocks of four lines, the complete chorus - you have to try whatever works best for your song.
Make sure the Catch button in the Marker Text window is enabled like this:
...so the text in the marker window will change at the given marker positions. If it is
off (grey) the current text will be displayed, regardless of the playhead position.