At its core, an MES is a real-time system that provides direction and instruction to the shopfloor and tracks all activity in the manufacturing environment, hence the "execution" moniker. The primary unit of track-and-trace is called Work In Progress, or WIP (the widgets you're making), and is often grouped into a logical and/or physical container called a Lot/Work Order.
An MES will also provide significant insight on factory performance by way of operational dashboards and KPI reports (Key Performance Indicators), the most common of which include yield, throughput and cycle time. These are often utilized as part of a lean manufacturing initiative designed to reduce waste, and therefore cost. The data being captured on the manufacturing line can be translated into actionable information and then brought to the surface so management has a clear picture of how things are running; pain points become clearer and inefficiencies can be improved.