In
the sentence: Fred came running toward them.
This
is a simple sentence. Because there is only one thought.
Sentences may be
simple (one independent clause), compound (two independent clause with
coordinating conjunction), complex (a subordinate & independent clause) and
compound-complex sentences (subordinate & two independent clause). The
benefit of complex or compound sentences is that it could give you more
explanation on the subject or topic of the sentence. This gives you a much more
understanding on what the sentence is trying to portray or to message to give.