Right. You came looking for football formations explained, and I'll wager you've already fallen down a hole of diagrams drawn by men in gilets describing shapes that need players you haven't got.
Let me save you the bother. A formation is a starting point, not a personality. It tells you where everyone stands for the kick-off and almost nothing after, because the second the ball moves it all changes. What actually matters is whether each kid knows their job and how it shifts when you've got the ball versus when you haven't.
So this is the honest version. Every guide below explains a real shape — what it does well, who it needs, and crucially when it'll let you down, because anyone selling you a formation with no downside is selling you something. Start with the 2-3-1 if you coach 7v7 little ones. Read the 4-4-2 one if you've been told it's dead (it isn't). And read the last one twice, because it's the one that matters most: why you should stop caring what you call it and coach the football instead.
Pick a sensible shape. Then forget it and develop the players.