A sharp axe is a safe axe. Dull axes not only make your work harder they can glance off the wood and cause serious injury.
Tools needed to sharpen an axe are a file, a honing stone, and a strop. A flat, mill bastard file should be used if your axe is extremely dull or chipped. After using the file (if needed) finish with a flat or puck style medium and then fine hone. Use a leather strop to complete sharpening your axe.