This is really easy on Linux, maybe even more that in Windows, you can use CRL+C and CTRL+V as in Windows, but the easy way is.

Select the text you want to copy, then go to the application where to want to paste it, and using the middle button of your mouse (the wheel in some models) you paste it.

Remember that to change from one app, to another you should use CRL+TAB, as if you use the mouse, you may loose your selection.