To quote someone else click on the 'quote' button on the top right hand corner of that users post. Then don't do anything to the tags, and simply add your own text after the tags. If you mess with the tags chances are that the quote might not work out as planned.
[quote = "mx_tifosi"]asdf[/quote]
And if you want to quote something that is not a thread post, simply click on the 'quote' button found in the menu when writing your own post (in the message body area). Insert whatever text you want in between the tags, and include a link outside of the quote tags (if necessary).
Questions or comments are welcome, especially since this is pretty basic explanation for normal quotes.