Mac OS X deals with file moving and copying similarly to Windows. When you drag files/folders between folders on the same disk, they are moved, and when you drag them between different disks they are copied. On Mac OS X it is a little bit harder to change the default behaviour when you are dragging and dropping files. On Windows dragging with the right click button will bring up a menu allowing you to select whether you want to copy or move, but on Mac there is no such option. Today I finally found the solution, which I wasn’t able to find on Google (shock horror!).
It is actually very simple to move a file from one volume to another (like a USB drive to your HDD) instead of just copying it. Simply drag the file from the source to the destination folder, and before you release the mouse button press the Command key. You will notice that the plus symbol and disappeared. When you release the mouse button your files will have been moved as opposed to copied! Quite useful for transferring things like images off a memory card.
Similarly, when dragging a file from one folder to another on the same volume, it will only move it. While this can be overcome using the Copy command in the edit menu, you can also do the same as above except hold down the Option key. A plus symbol will be added to your cursor, and when you release it will be copied to the destination folder instead of moved.
While I’m sure many longtime users will know this, hopefully it will help a Mac newbie like me