dividing the page equally

Click on "photoshop" next to "file" "edit" etc on the top bar and click preferences and go to grid guides etc. Click on the drop down menu in the grid section and select percent (it will most likely be on cm's or inches)- set the value to 33.3 (to split it into thirds). Click view - show grid and it will divide any size page into thirds. Magic. Also set snapping to grid and you can draw very accurately.