Moon rotates once in its orbit so that we see same side whatever
the phase (called tidal locking, later)



What is happening  during eclipses        ...                                     and what you see

Moon's orbital plane around earth is inclined by 5 degrees to ecliptic, and
intersects ecliptic plane along the "line of nodes"

If earth, moon & Sun are lined up on this line, get eclipse. Usually not,
so eclipses are rare.

Retrograde Motion of Mars