When you want to quote something that you have cut and pasted into the middle of a post, look at the icons above the text field and find the "bubble" like the thing they use in comics to put the words of whoever is talking. It is between the # sign and the icon with the mountains and sun.
Within your post, highlight the text you wish to quote, then click the quote-bubble icon. It really is that simple!
If you do not see a row of formatting icons with this symbol, click "Go Advanced" underneath the text field and you will see all the buttons.