KERNEL-MODE

The kernel-mode programs run in the background, making sure
everything runs smoothly - things like printer drivers,
display drivers, drivers that interface with the monitor,
keyboard, mouse, etc. These programs all run in such a way
that you don't notice them.

When the computer boots up, Windows calls the KERNEL, the
main kernel-mode program that allows all the other programs
to run, even the user-mode programs.

USER-MODE

These are the programs that you run when you want specific
programs - e.g., MS Paint, MS Word, and Calculator. These
are heavily restricted, as to not crash the system. Windows
uses memory-protection services offered by the processor to
prevent malicious programs from interfering with the rest of
the system and corrupting it.