Division has two interpretations: (1) Sharing: 12 cookies distributed equally among 3 friends gives 4 cookies each. (2) Grouping: 12 objects grouped into sets of 3 makes 4 groups. Both yield 12 ÷ 3 = 4, but the context and question differ.
You already have experience with both sharing things equally among friends and making equal groups — now you are connecting those two ideas to the same mathematical symbol: ÷. Division is the operation that answers the question "how do I split this into equal pieces?" and it comes in two flavors that feel different but produce the same arithmetic.
The first interpretation is equal sharing (also called partitive division). You know the total and the number of groups, and you want to find how much is in each group. "12 apples shared equally among 4 children — how many does each child get?" You are distributing the 12 one at a time across 4 groups until they're gone: 12 ÷ 4 = 3 apples each. The number you're dividing by (4) is the number of groups.
The second interpretation is equal grouping (also called measurement division or quotitive division). You know the total and the size of each group, and you want to find how many groups you can make. "You have 12 apples and put 4 in each bag — how many bags do you fill?" You are measuring out groups of 4 until the 12 are used up: 12 ÷ 4 = 3 bags. Here the number you're dividing by (4) is the size of each group, not the number of groups.
Both problems use 12 ÷ 4 = 3, but they ask different questions. Reading division problems carefully — "how many *in each*?" versus "how many *groups*?" — tells you which picture to draw in your head. This is the same distinction you practiced in 2nd grade, just now with larger numbers and the formal division symbol. Building both mental pictures makes you flexible: you can approach any division story from the angle that makes it easiest to visualize, and you'll recognize that the answer 3 means something slightly different depending on what was asked.