The following screenshot was taken with my secondary Windows 10 installation booted.
Note that (C:) changed from "Win10 ProA" booted in the default installation to "Win10 ProB" booted in the secondary installation; the unloaded system drive becomes (A:).
My partitioning scheme has evolved and morphed over the last couple of decades, and most users probably don't need this degree of partitioning, but I recommend at the very least four partition; OS, Program Files, Users and Data. That level of partitioning makes drive imaging and restoration of images more granular and much quicker. If your OS gets pooched, just restore a drive image of it from an earlier date, and that won't affect the other partitions at all.