Dell MFP Laser 3115cn: where is legal paper loaded? Where is tray 1? How is it loaded in tray 1?

if the 3115 is anything like the 3110, and i understand your question correctly, tray one is on the bottom of the printer like most other dell printers. and the switch to legal size paper you have to pull the drawer completely out of the printer. on the back of the drawer is a blue tab with an arrow pointing towards the front of the tray. push this tab and pull back on the end of the tray to extend it for legal sized paper.

That's it.  Thank you.