Can you explain the differences in these terms, and the function they serve when writing an essay?

Question

thesis and thesis statement
central reasoning and central relationship

The thesis is your central idea, your main idea, the point you are trying to prove in your paper. The thesis statement is the one sentence in the paper in which you state this idea.
http://grammar.ccc.commnet.edu/grammar/composition/thesis.htm

Central reasoning -- I haven't heard that term before, but it seems as if it would include the primary reasons (evidence, examples, data, etc.) you are using to prove your thesis.

Central relationship -- I haven't heard of that one before either.

Here are some grammar/writing websites where you can try to look up various terms:
http://grammar.ccc.commnet.edu/grammar/index2.htm
and
http://leo.stcloudstate.edu/catalogue.html
and
http://nutsandbolts.washcoll.edu/
(Use the column at the left as the table of contents.)

=)