Once you get the USB stick working you can try Ubuntu as a live operating system to make sure it works ok on your machine before installing to the hard drive.

If and when you reach the point where you decide to install to your HD then it is usually fine just to choose to install alongside Windows and then to accept the defaults that the installer suggests. Ubuntu will do all the partition modifications without you needing to worry about it. Deciding whether you want to Install instead of Windows or alongside it is the only intervention you really need to make, and it will clearly ask you that question.

Oh, and if you do install it permanently on your hard drive, remember to remove the USB stick when you reboot or it'll boot from the USB again instead of from the on-board installation.