Modern computers allow running multiple programs at once, each in its own window. The taskbar (Windows) or dock (Mac) shows all open programs and windows. You can switch between them by clicking in the taskbar or using Alt+Tab, and resize or minimize windows as needed. Effective window management is essential for multitasking.
From your study of operating system fundamentals, you know the OS is a layer that manages hardware and software on your behalf. One of its most visible jobs is managing windows — the rectangular panels that programs use to display themselves on screen. Think of the screen as a physical desk: each window is a piece of paper on that desk. You can overlap papers, move them around, make them bigger or smaller, or temporarily set one aside in a drawer. The operating system is the desk itself, keeping track of where everything is.
The taskbar (on Windows, along the bottom of the screen) is your master list of what's open. Every running program gets a button there. Clicking that button brings that program's window to the front — it doesn't open a new copy of the program, it just shifts your attention to the one already running. The taskbar also shows a clock, system status icons, and a button to see all open windows at once. On a Mac, the equivalent is the dock, which works similarly.
Windows have three standard controls in the top-right corner (Windows) or top-left corner (Mac): minimize hides the window from the screen but keeps the program running (it reappears when you click its taskbar button); maximize expands the window to fill the entire screen; and close shuts the program down. Minimizing is especially useful when you have many things open — it clears the clutter visually without stopping any work in progress.
The fastest way to switch between open windows is the keyboard shortcut Alt+Tab (Windows) or Command+Tab (Mac). Hold the first key and tap the second repeatedly to cycle through all open programs in a visual switcher. This is much faster than reaching for the mouse and clicking in the taskbar, especially when you are moving back and forth between two programs frequently — like a web browser and a document you're writing. Practicing Alt+Tab until it becomes reflex is one of the highest-leverage digital literacy habits you can build.