In particular, it probably has its focus policy set to "click to focus." This means that in order for a window to gain focus (become active) you have to click in the window. This is contrary to traditional X windows behavior. If you take my advice and get a 3-button mouse, you will want to set the focus policy to "focus follows mouse". This will make using the text copying feature of X windows much easier to use. You may find it strange at first that windows don't raise to the front when they get focus (you have to click on the title bar to do that), but you will enjoy being able to work on more than one window at once without having the active window obscuring the the other. Try it and give it a fair trial; I think you will like it. You can find this setting in the configuration tools for your window manager.
Could somebody help me do this in Mint? *focus follows mouse*
With love and gratitude - No-Thing