When you download a Soundpaint instrument, you will find 2 separate lists of sounds. You can switch between these two lists with the "Programs" and "Parts" buttons near the top left corner of the interface.
Parts are the individual sounds, or the building blocks of programs. For example, a single part of an acoustic instrument will be one articulation (staccato, legato, etc.) and one microphone position (close, decca, etc.). For analog synths, a part may be a single waveform. Parts load into the 4 large boxes in the center of the Soundpaint interface. They will load over whichever box is currently highlighted, so make sure to click on an empty box if you want to add a part to the program you are using.
Programs are presets created with 1-4 parts, with the Rack, Effects, Arp, and Matrix, and any modulation settings saved as part of the Program. The name of the program will appear above the 4 part boxes.
If you want to build your own program, you can make changes or add parts to existing programs, or right-click on the program name at the top of the interface and select "New Program." This will clear all parts, effects, and other settings, allowing you to start fresh, or audition individual parts without any extra effects applied.
To save your own programs, select "Save program to user library" from the hamburger menu in the top left, or by right-clicking the program name at the top of the interface. You can switch between the factory and user directories with the 2 buttons above the Program & Parts buttons, in the top left corner.
You can find more information on parts and programs in the overview video below.