Feeding rodents is pretty easy. Most subsist primarily on commercial pellets and water. Some rodents need supplementation with hay and fresh veggies, like guinea pigs and degus. You can provide treats in moderation for any rodent pet, being careful not to feed too much sugary fruit, as rodents can also get diabetes.
The main challenge with animals that need fresh food is keeping it stocked, since leafy greens and vegetables are quite perishable. It can also be challenging in the beginning to learn what veggies are safe for your rodent. And it sounds like a little thing, but cleaning and prepping the food can also be somewhat time-consuming.