If you're new to the Terminal, Pasting Commands probably seems like a godsend. Until it doesn't work. Here's how to do it properly.

Cutting, Copying and Pasting:

This is actually very simple to do.
In most applications Cut, Copy and Paste are Ctrl + X, Ctrl + C and Ctrl+V respectively.
In the Terminal, Ctrl+C is Cancel Command. The others do things to, but that's not important.
To paste (probably the one you'll use the most), use Ctrl + Shift + V.
Use X or C appropriately for cutting and copying.

Congratulations, you have just learnt how to Cut, Copy, and Paste in the Terminal in Ubuntu!