Copy text by highlighting it with your mouse. Usually you can use Ctl+C or right click the selection select "copy" from the popup menu as well.
Paste text by clicking your middle mouse button. Ctl+V also works in many places and so does Shift+Insert.
What to do when that doesn't work
The problem occurs when different applications use different clipboards. You will successfully copy the text to a clipboard in Application A, but when you go to Application B to paste, it will try paste from a different clipboard. In Windows all applications use the same clipboard.
There are several solutions. Probably the easiest one to get working is to install Parcellite.
sudo apt-get install parcellite
A clipboard icon will show up in the system tray.
- Copy some text.
- Click the clipboard icon in the system tray and select what you want from the menu.
- Paste your text.