First: Clean up your audio tracks!
Create separate tracks (in this order) for:
The Advanced Authoring Format (AAF) is a professional file interchange format designed for the video post-production and authoring environment. It was created by the Advanced Media Workflow Association. (Wikipedia)
AAF exports usually are used when you send your project to a sound editor, sound designer or a sound mixer. Because effects get lost in that process a multitrack mixdown export (or a simple stereo mixdown). AAF is the "never version" of OMF and can store and transfer volume automation data and clip names (OMF couldn't). But you still lose all plugins and most sfx plugins.
The sesx files are proprietary to Adobe Audition and can not be opened with any other program (of my knowledge). Still it is a convenient way to archive your projects and gives you the opportunity to export the audio source files you used in your project trimmed with handles (meaning it only exports the part you actually used + some room to make slight changes if needed).
Professional audio mixing is a bit more complex on many levels. One of those is correct and standardised separation of differently routed audio channels. The article on the following link is a good start if you are interested.
We are not asking you to do this in this course!