Do I need to format any drive for installing Ubuntu?

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http://askubuntu.com – I just wanted to try Ubuntu and I downloaded the .iso file. I want to have both windows and Linux on my PC and although I read the tutorials and other topics in the site, I didn't get the answer to one question. For installing it alongside Windows (assume that Windows is in drive C), and not installing it in the same drive, But in drive G for example, do I have to format that drive or that will not be necessary? ( the other drive is in NTFS format) When we are "selecting drive", does it mean selecting one of C or D or ... partitions? And what does the space allocation means? (HowTos)