One-way traffic means that all the cars and vehicles on the road are going in the same direction. It's like everyone is going in a big line, following each other. Imagine if you and your friends were all walking in the same direction on the sidewalk, you wouldn't have to worry about bumping into each other.
One-way traffic is usually used on busy roads or streets to make it easier for drivers to get to where they need to go. It also helps to reduce accidents because everyone is going in one direction and there is no worry about cars crashing into each other.
When you see a one-way street sign, make sure you go in the right direction. You don't want to go the wrong way and cause an accident or get a ticket. It's just like following the rules in a game, everyone has to obey them to have fun and stay safe.