Can not paste into terminal
I'm relatively new to linux.
My question is, why when I do ctrl+C (copy) in Eclipse, and then shift+insert (paste) in command line, there's nothing pasted?
If you mean the GNOME Terminal, the shortcut for paste is Shift+Ctrl+V. (See the Edit menu).
There are actually multiple paste buffers (or clipboards if you prefer).
When you mark some text using the left mouse button, that text is immediately put in the primary paste buffer. You use the middle mouse button to paste from the primary buffer.
The secondary buffer is generally copied to by marking the text and hitting Ctrl+C and pasted from by hitting Ctrl+V, though these key bindings are only a convention; some applications require different key bindings.
The terminal has already mapped Ctrl+C|V to mean something else, so Shift+Ctrl+C|V has been chosen for this instead.
There is also a third paste buffer, but this is rarely used.