Last season Andy Pohl—who was the assistant principal and athletic director at an elementary school in Chicago—asked me to visit his youth basketball practices, specifically the 4th, 5th, and 6th graders.
When running their offense, I heard all the coaches say "screen, screen.” The kids looked at them like they were speaking a foreign language. The coaches assumed that the players already knew what a pick or screen was, but that is a bad assumption.
If kids watch basketball, they watch the ball and the player who has the ball. It is the coaches' responsibility to teach players about screening. Teaching players to screen and how to cut off of screens are the most important components in building a scoring team offense.
Screening means just what it says, trying to pick off defenders in order for another player to get an open shot or initiate the offense. Once a screen is established, the screeners must maintain their spot and not move or lean into the defender. Only after the cutter goes by the screen can the screener move again.
Again, it is also the coaches' job to teach cutters the footwork necessary to run their defender into the screen. Ineffective screens are usually the fault of the cutter.
The most knowledgeable coaches will know the various types of screens—up/back screens, down screens, cross screens, diagonal screens, post screens, rubs, ball screens, and double ball screens—and work with their teams to execute them consistently.
Learn them all and teach them well. Your offense and players will benefit greatly.