A+: Task Bar and the Tray
The Tray, Notification area, System Tray or SysTray is the expandable bit at (normally) lower right which holds the Clock as well as icons for other always-running apps you need to interact with, such as the Speaker icon for sound control, the Safely Remove Hardware icon for un-mounting USB flash drives, and the Wireless icon on laptops to show if you're connected and how much signal strength you have.
To the left of the Tray you may see other components; the most popular to the left of the Tray is the Language Bar, which unless you do computer dictation is of little use, then the Task Bar itself, which tells you what programs are running, followed further to the left by the optional Quick Launch (which is highly useful and shows very frequently used apps for a very quick start). At farthest left is always the Start button where you invoke the start menu showing a path to all apps and all settings.
Always, that is, unless you click and drag the inside the bar from its customary position at the bottom to the top, left or right, where it will stick and stay, or if you enable Auto-Hide (in which case the toolbar will disappear when the cursor is not within its area, or if you disable Keep the taskbar on top of other windows in which case it will only appear when an app is not maximized. The Task Bar can also be expanded by click-and-drag of its top edge to show more than one row of apps, so the icons for running apps can show the file they're working on.
Locking the Task Bar prevents it from being moved or resized by accident and is highly recommended.