Easy difficulty is Ghost Babel with training wheels.
More resources spawn
Some bosses become easier
Snake is built like a tank, needing a ration is fairly unlikely.
Fewer guards and cameras
One of the awkward aspects of Easy is that Alerts and Evasions clear faster than other difficulties.
Guards without body armor die in 1 bullet, 2 bullets with body armor.
Guards without body armor will die immediately if you triple punch them.
Tutorial of Outside Stage 04 and Stage 05
Tutorial of Stage 06, Stage 07, and Stage 08
Tutorial of Stage 09 and Stage 10
Tutorial of Stage 11, Stage 12, and Stage 13