Further to the above, I think you are trying to correlate modes with thrust lever movements.
If you are in approach mode with the autopilot in, and you move the thrust levers to "TOGA" (ie. full power, TOGA= (TakeOff/GoAround) then the automatics will give you full power and also follow the go-around track, provided this is in the computer already. The mode will change to "Go-Around Track". You can of course take it out of go-around track should you want to fly a heading say.
Bascially, the aircraft is reading what you want to do. It says, well, you are on the approach and now you want full power so you must want me to go-around, and that is what it will do, unless you stop it.
As mentioned, TOGA is only really used for TakeOff (when full power is needed) and for Go-Around situations.
Otherwise you remain in Climb detent, which is basically autothrust active "mode" and would I guess be the same as in a Boeing except the levers themselves don't move.
Pushing the thrust levers to the full forward "TOGA" position will always give you full power.
FLX/MCT, the middle gate, is used for take-off (as mentioned) and also in the event of an engine out condition.
On the take-off you can still go TOGA, one example is if you forget to set an assumed temperature, and you start the take-off roll, you would not abort (although it has been known), you would just go full forward to TOGA power.
Say you are doing a Flex take-off (reduced power) and you had an engine failure on take-off, then you would push the thrust leveres full forward, into TOGA detent, thus giving you full power on remaining engine.
At the appropriate time you would bring the thrust back to MCT (Max Continuous Thrust) on the good engine.
Alternatively when flying you can of course disconnect the autothrust and then the thrust levers are just like regular thrust levers.