Dear Bob,
I hope you were able to finish up your assignment... but for future reference, prepositions are words that "pre- position" other items...
aboard
about
above
across
after
against
along
among
around
at
And so on. :) There are plenty of lists out there on the interwebs (and some you just have to memorize), but some of the most common are as follows:
at
in
to
off
on
of
for
from
around
about
over
Additionally, keep in mind that a PREposition has to come before something. The something is called the "object" of the preposition. For example, in your poem, you said, "I am touched by the miracle God has provided to my family." There are two prepositions there: by and to. What were you touched by? The miracle. To whom did God provide the miracle? Your family. So, "by the miracle" is a prepositional phrase, with by as the preposition and the miracle as the object of the preposition. "To my family" is also a prepositional phrase, with to as the preposition and my family as the object of the preposition.
Hope this helps!