Hey Bin,
Not sure what you're using computer-wise but I think it should be fairly straight forward.
To separate your lines just press return, I don't want to patronise so don't be offended if I am but 'return' is the big key with the right angle arrow on the right of the keyboard.
To quote other people, click the quote box on the bottom right corner of the post that you want to quote. That text will then be inserted into your box and you can just type below all that text ( make sure you start typing after the word 'quote' in brackets). If you only want to quote a small part of someone's comment, just delete the bits you don't want to quote, remember to leave the jibberish computery text at the top though or it won't work.
You can click on preview (next to post) to check how it all looks.
Hope this helps
Hab..