In just about every application, including the Finder (the OS):

1. Select whatever you want to copy, usually by dragging over it. Double-clicking in apps that conform to the standard selects whole words. Double-clicking and then dragging extends the selection by whole words. Selecting in graphics programs varies, but may involve clicking on graphic objects and/or selecting a tool and then dragging over the area to be selected. Once you get into heavy use of Photoshop and other complex programs, selecting is a whole chapter in the manual.

2. Choose Copy from the Edit menu. Keyboard shortcut is command (or Apple, the key on either side of the space bar)-C. Some apps, such as Microsoft Office, may also have a toolbar with an icon for this.

3. Click where you want to paste it.

4. Choose Paste from the Edit menu, or command-V. Ditto for toolbars.

(In other words, pretty much like Windows.)