OS X Yosemite: drag and drop
You can drag and drop to do just about anything on your Mac: move files and folders to new locations, add a photo to an email message, or move a chunk of text in a document. You can also drag items to the Dock or a Finder window sidebar so you can get to them easily.
To drag an item, select it, then hold down the mouse or trackpad button while you drag it to a new location. Release the button to drop the item into place.