In order to install Ubuntu, you must obtain an installation CD. There are numerous ways of doing this, and the method you use will depend on what is available to you.
The Ubuntu installation CD is available to download from the Ubuntu website as a CD image (.iso). Visit the Ubuntu website to download a copy.
You will be asked to choose the version you want, Desktop or Server (Server supports Linux, Apache, MySQL and PHP out of the box). You will also need to choose from the latest version or the LTS (Long Term Support) version.
Select the architecture you want and a server to download from that is near you.
There is also a check box at the bottom that lets you download the Alternate Desktop CD. This has a text based installer for computers with lower memory.
The CD image is a large file and may take several hours to download. If you have a slow Internet connection (such as dial-up), it is recommended that you obtain a CD by some other means (see the following sections).
Once you have downloaded the ISO file, you must burn it onto a CD. In order to do this, you will need suitable CD-writing software. Full instructions on burning the ISO file to disc are provided on the Ubuntu support website.
It is possible to buy an Ubuntu CD from a third party, for a (typically) small charge. While these third parties are likely to be selling Ubuntu CDs for their own profit, you may find that buying a CD is the most convenient option for you.
Click the Buy Ubuntu on CD tab on the Ubuntu website for more details.
Ubuntu offers the ShipIt service, which will deliver a small set of Ubuntu CDs to you at no cost. Follow the instructions on the ShipIt website to place an order - delivery will typically take 6-10 weeks.
Ubuntu is freely available software libre. You are encouraged and legally entitled to copy, reinstall and redistribute your copy of Ubuntu, and so if you know someone who will allow you to borrow their Ubuntu CD, then by all means do so! If you have a local Linux user group, they may also be able to provide an Ubuntu disc for you.