Vinny, music theory is a whole subject into itself and takes years to study and learn, just like learning an instrument.
When you study from my How To Play Saxophone” book you are learning some basic theory as you go along.
Reading music and understanding intervals and scales, chords etc is all part of music theory.
To your question regarding transposition, I wrote an entire article telling you how it relatyes to the saxophones and concert pitch (piano) here:
https://howtoplaysaxophone.org/saxophone-keys
Simply put, you’re playing an Eb alto so when you play a C on it, it’s really an Eb on the piano. To fully grasp this look at a keyboard. Then touch the Eb, then count down all the notes to the C. You will count 3. These are semi-tones: D, Db and C. Now you can transpose any piano not to the proper alto note.
