The Basic run down is this.
P220-Full Sized .45 Semi Auto. Available in Nitron or Stainless Steel.
P226-Full Sized 9mm, .357sig, and 40 S&W. Many variations with minor differences.
P229-Mid sized to Full Sized 9mm, .357sig, 40 S&W. Also many variations.
P239- Compact 9mm, .357 sig, .40 S&W. Fewer variations
2022- Polymer Full Sized
Those are the basic mainstays of the Sig Sauer offering. Variations include grip type, All stainless vs some stainless. Regular Single action/double action vs double action only trigger (AKA DAK). Some differences are cosmetic like Equinox and so forth.