To "divide evenly" means that one number can be divided by another without anything left over.
In other words no remainder!
Example: 6 can be evenly divided by 2 (3 times exactly)
But 7 cannot be evenly divided by 2, as there will be one left over.
Note: "evenly" in this case means "fairly" or "exactly", it has nothing to do with even numbers, for example 15 can be evenly divided by 3 (5 times) and they are all odd numbers.