To divide you are basically taking something and putting it into groups. For example, if you have 20 divided by 5, you can look at it like this.
20 apples and 5 baskets, you place one apple in each of the 5 baskets. Than you do this again until there is an even amount of apples in each basket and you don't have any outside the baskets.
So what if you have 24 apples and 5 baskets. You could do the same steps but your going to have a remainder of 4 apples because 4 apples wont fit into 5 baskets without you cutting them.
And also if you have say, 21 apples and 5 baskets you can go through the same steps but you can cut the remainder apple into 5 equal peaces to get 4.2.