Well, thanks to the wonderful people at tegger.com you can read the
best and most easily understood explanation I have ever seen. Here
is an example of the diagrams they have provided...

http://www.tegger.com/hondafaq/mastercylinderreplace/howworks.html
While this may be a Honda site, the brake information is generic and
equally applicable to your AE86 (and many other cars). I highly recommend
that if you want to learn about brakes, you visit this site and browse the
excellent information provided.
Cheers... jondee86