so a quick listen and I knew the chord type straight away m7/4 in this case Gm7/C or 6/2 in this case Bb6/C aka C9sus4 - a typical disco period chord (start of many different songs including the hustle)
horn line is C-C-Bb-A-Bb-C-G and variations thereon
this is really simple applied aural skills - helped that I have played the opening chord a few thousand times on guitar and keys, but ultimately the same skills that allow me to decipher the melodic line come into play: rhythm, intervals, tonality
to acquire these skills will take some time but you can make a start at
teoria.com with their ear training and theory drills
once the song kicks of the harmonic material is slightly more complex a there are two disparate ideas running the chords vs the bass
bass moves C-C-D whilst the chords go C/D-Dm7 then it all moves up a 4th to F-F-G whilst the chords go F/G-Gm7 then back to the previous phrase then the opening chord before moving into the chorus which is based around Gm7 wit a bass line that ultimately descends back to the C/D-Dm7 phrasing
Notes in chords
Gm7/C ~ G-bB-D-F over a C bass
Bb6/C ~ Bb-D-F-G over a C bass
C9sus4 ~ C-F-G-Bb-D - this is the most accurate voicing although the G is on top i.e. C2-F2-Bb2-D3-G3
C/D ~ C-E-G over a D bass
Dm7 ~ D-F-A-C
F/G ~ F-A-C over a G bass
Gm7 ~ G-Bb-D-F
octave numbers note
middle C = midi note number 60 = C3 in most daws = C5 in fl and BiaB