Many mice have a middle mouse button. On a mouse with a scroll wheel, you can usually press directly down on the scroll wheel to middle-click. If you don't have a middle mouse button, you can press the left and right mouse buttons at the same time to middle-click. If you find you are unable to middle-click this way you can try following.
Some touchpads have a middle mouse button and some do not. On touchpads that don't have a middle mouse button you can middle-click by tapping once in the top right-hand corner of the touchpad. You have toin the touchpad settings for this to work.
Many applications use middle-click for shortcuts:
One common shortcut is to paste selected text. (This is sometimes called primary selection paste.) Select the text you want to paste, then go to where you want to paste it and middle-click. The selected text is pasted at the cursor position.
Pasting text using middle-click is completely separate from the normal clipboard. Selecting text does not copy it to your clipboard. This quick method of pasting only works with middle-click.
On scrollbars and sliders, a regular click in the empty space moves by a set amount (such as one page) in the direction you clicked. You can also middle-click in the empty space to move to exactly the location you clicked.
You can quickly open a new window for an application with middle-click. Simply middle-click on the application's icon, either in the Launcher on the left, or in the Dash.
Most web browsers allow you to open links in tabs quickly with middle-click. Just middle-click any link, and it will open in a new tab. Be careful clicking the link in the Firefox web browser, though. In Firefox, if you middle-click anywhere except on a link, it will try to load your selected text as a URL, as if you used middle-click to paste it to the location bar and pressed Enter.
In the file manager, middle-click serves two roles. If you middle-click a folder, it will open in a new tab. This mimics the behavior of popular web browsers. If you middle-click a file, it will open the file, just as if you had double-clicked.
Some specialized applications allow you to use middle-click for other functions. Search your application's help for middle-click or middle mouse button.