how to copy item on screen

Command+Shift+3 captures the entire screen, Command+Shift+4 and then use the cross-hair cursor to outline what you want to capture...both give you screen shots you can then insert or drag and drop.

A neat, tidy way to grab things like dropdown menus is to open the menu, then press Command-Shift-4 and release, then press the Spacebar. Then when you move the cursor over a window the entire window will be selected. For this purpose, a menu acts as a separate window. When the menu is highlighted (turns bluish), click the mouse.

Examples -

Safari menu -

Control-clicking the dsktop -