The 2 most important commands in windows (Mac-heads are on their own):
Ctrl + C copies to clip board
ctrl + V pastes from clip board
Bonus: ctrl + X copies to clipboard and erases from current window.
So, find the post, highlight the address line at top, press and hold the ctrl key, then hit the c key. Change windows to the post you are working on, place the curser where you want it and hold the ctrl key and hit the v key. Done!
Edit-to copy text in a post, highlight the desired text, then do the same thing.