It's common for a microcontroller to have many fewer A-D converters than it has analog pins, with an analog multiplexer in between the pins and the A-D converter.
Yeah that makes perfect financial sense, THE ADC will be relatively expensive so one ADC can be used via a mux to read different pins on the same port
The STM32F4 actually has three separate A2D converters, each with an 8:1 mux (and some complex connections to pins that I didn't look into very much.)
Got that bit the STM32F4 has ADC1 ADC2 ADC3, I dont know much about their associated mux block though
So you could read up to three Analog inputs without messing separately with the muxes (except at setup time), or you'll have to do something similar to what the Arduino core SW does.
I am reading three separate ADC's but I had to set them up on separate ports, port A port B and portC, I really havent a clue how I could setup the mux so that I can use say three ADC's on one port it just wouldnt work even better would be to use one ADC on one port with three separate pins but I havent a clue how to do that, at the minute I am still on a high because I got an input recognised by the board (dont spoil it!!) the analogue reference is 2.95V and I wish I knew how to change that but for the moment I am happy!
In general, it is a useful technique in learning a new processor/board to try to COPY (only be sure to call it "port") an existing familiar set of software. So the question shouldn't be "how do I read analog inputs on STM32F4?", but "How do I duplicated the AnalogRead() function on STM32F4?" It may seem very similar, but the process is different. Instead of starting from scratch, you get to look at the steps that the arduino code uses, and figure out whether they have equivalents on the STM. Since the individual steps are smaller, they may be easier to understand. Of course, you end up needing to understand both the existing Arduino code AND the new processor code. But ... it's good for you!
I would be willing to do that in fact I would go as far as to say I would probably enjoy it!,...
trouble is I havent got a clue where I would even start!