Basic Back+Fierce Combos
Back+Fierce --> Fierce Kikkoken
Back+Fierce --> Short Spinning Bird Kick
Back+Fierce --> Forward Spinning Bird Kick
Back+Fierce --> EX Spinning Bird Kick
Back+Fierce --> Fierce Kikkoken --> Hoyouku-sen
Back+Fierce --> Hoyouku-sen
Back+Fierce --> Fierce Kikkoken --> Hoyouku-sen --> Superjumpcancel --> Fierce --> Fierce
Back+Fierce --> Houyouku-sen --> Superjumpcancel --> Fierce --> Fierce
Conditional Back+Fierce Combo (Only works when the opponent is jumping in on Chun Li)
Back+Fierce --> EX Lightning Legs
Useless Back+Fierce Combos
Back+Fierce --> Taunt
Back+Fierce --> Kikou-Shou
Back+Fierce --> Tensei-Ranka
These are the basic Chun Li combos that most Chun Li players need to know. In the basic section I ordered them from least damaging to most damaging. In order to execute the Back+Fierce into SBK, Charge down, do quarter circle back - hit fierce, quarter circle up - hit the appropriate kick button. You could even get fancy by charge partitioning the first charge --> down parry --> Back+Fierce --> SBK, but if you are already learning charge partitioning, you should be playing as Urien.
I did leave quite a few Back+Fierce combos out, because these were just variations on the basic ones. There are a few different things that you can do after superjumpcancel, but those are advanced mind games. Mainly it depends on where you want Chun Li to land in relation to your opponent after you get out of the air.
I will end this post with the most damaging Back+Fierce combo.
Back+Fierce --> Fierce Kikkoken --> Houyouku-sen --> Superjumpcancel --> Supercanceled Houyouku-sen
This combo is useless because the damage scaling function of the game engine makes the second Houhouku-sen do meager damage. Better to do Fierce --> Fierce.