How to lay rebars for a 4'x4'x12" footing for a column?
Keep the rebar 3”” from the bottom of the footing and 3” from the edge of the footing. 

I’d install the #4 bars 8” oc each way. (You’re not concerned with flexural bending of the footing, because the column on the footing is so large 24”x24”). 

I would run 4 - #4 rebar vertically in the column and install 4” hook (90 degree bend) in each rebar and extend it into the footing 8”.  Make sure the vertical bars are about 1” clear from the edges, so concrete can encapsulate the rebar. 

For that height of column, I’d use #3 ties at 12” oc. (#3 rebar you can bend by hand.) 

I don’t know what you’re supporting (how much load), but that will support about 30 kips at each footing, unless you’re located in a swamp, like me. And the footing will weigh about 7 kips (dead load) each. 

Keep all rebar down 3” from the top of the column.