How to create a blinking effect in After Effects CC? What I want to do is simple conceptually, but I am just not having success with actually doing it.

I am creating a short video snippet in After Effects, as part of a larger presentation. The video is supposed to begin with a blinking light under the title, which then transitions, with a sound effect, to the video itself.

I've worked out the sound effect, the transition, and all of the other stuff - I just don't know how to animate a blinking light. There must be a way to automate turning the opacity on and off - but all of the tutorials I've found date from several years ago at the earliest and presuppose a working knowledge of After Effects that is more in-depth than what I have.

Can someone point me in the right direction? Preferably with explicit steps!
Create your keyframes
Select them by holding down Shift, via box select or simply click the Flare Brightness Property
Then hold Alt and click the stopwatch icon, this will create an expression
Then click the Expression Arrow > and select Property >  loopoutduration this will cause that the keyframes to repeat themselves