Check the Help for:

• track changes
• insert comment
• character styles

For the activity you describe, track changes may be less messy than inserting comments … but bear in mind that if you aren't reasonably disciplined about exactly how and where you add your notes it can be a nightmare trying to see the wood for the trees afterwards.

Using your own character style for your comments might be easier to manage. Ctrl+shift+s is a quick way to apply styles, or you could set a shortcut key.

Personally, I'd print off my outline and add notes in pencil for typing in after the lecture <g>