Adjust the double-click speed
Double-clicking only happens when you press the mouse button twice quickly enough. If the second press is too long after the first, you'll just get two separate clicks, not a double click. If you have difficulty pressing the mouse button quickly, you should increase the timeout.
Click the icon at the very right of the menu bar and select System Settings.
Click Mouse and Touchpad.
Under Double-Click Timeout, adjust the Timeout slider to a value you find comfortable. Use the smiley face under the slider to test your settings. A single click will make it smile. A double-click will give it an ear-to-ear grin.
If your mouse double-clicks when you want it to single-click even though you have increased the double-click timeout, your mouse may be faulty. Try plugging a different mouse into your computer and see if that works properly. Alternatively, plug your mouse into a different computer and see if it still has the same problem.
This setting will affect both your mouse and touchpad, as well as any other pointing device.