I'm not sure if I got your question, but if you're using Windows is very simple:
1. With the mouse, select the code they ask you to paste.
2. Right click mouse
3. Click "Copy" from the contextual menu appearing
4. Go to where you need to paste it
5. point to where you need the code to be
6. Right click mouse
7. click "Paste" from the contextual menu appearing on right click

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or, using Keyboard:
1. select the text
2. hit CTRL+C
3. go to where you need to paste and hit CTRL+V

that's it
let me know you need any help !
All best,
Radu