I have a worksheet that I am working on that has 13 pages. 12 pages
that represent the months in the year and the 13th page is the
planner page. On the planner page there is an area where the user
may select a month and on that portion of the planner worksheet I
would like for it to be able to populate the planner work sheet
with the percentages from the same month the user is requesting.

... A43 is where the user can select the month from a drop down
list. A45 is where the results should show from pulling from the sheet
labeled matching the month the user has selected.
C3 is the cell on the sheet of the selected month of the user.

Here's one way.

In the A43 drop-down list use the same names that are the tab names;
maybe, Jan, ..., Dec.

Then in A45 put
=INDIRECT(A43&"!C3")