This tip is for Windows users -- any version of Windows. Many of you might be familiar with it already but I personally have met many who aren't, so here goes.
The most common way to move data around your computer is via drag-and-drop. That is when you click on one or a more selected files, then, while keeping the mouse button held down, drag them to a specified location and then drop them (by releasing the mouse button) at the location of your choice.
When you drag items from one folder to another within a drive (most of the time, everything on your computer is stored on a single drive), they will be moved to the destination folder, meaning they no longer reside in the original place. But if you drag items from one drive to another (such as from your desktop to an external drive connected to your computer's USB port) they will be copied to the destination instead, meaning you will have two identical versions of the data, one in the original place and one in the new location.
What if you want to decide when drag-and-drop moves the data or copies it? It's easy: Instead of using the left mouse button, use the right mouse button for the dragging. Now when you release the mouse, you will be prompted to choose whether you want the file moved or simply copied.
Try it! This will come in very handy when you want to make a copy of files or folders when working within your computer's local drives, or if you want to quickly offload data to an external drive to increase the free space on your computer's main drive.