Theres two easy ways to do this. Open up your bookmarks manager (Ctrl+Shift+B) and simply left click and hold somewhere in the main windows that is not a folder or bookmark and drag over the files you want to select. Around the edges is the easiest place to do this. You can then drag and drop them around just about anywhere you want. Another way to do it is to hover the mouse of the folder or file you want to select. You should see a check mark appear on the left side of it. Click that check mark so it turns blue and that entry will be selected. You can select multiple entries this want and then drag and drop again.
