The Elementary OS website is a good example as to how websites should be created. It is simple to navigate and easy to use. The content is up to date and the content is clear and readable. There is also a very good support area.
In order to download Elementary OS you just have to scroll beyond the screenshot on the homepage and click the "Download Freya" button.
Hold on a minute though! If you press the "Download Freya" button you will be asked to make a payment of $10.
Just above the "Download Freya" button there are buttons showing $5, $10. $25 and Custom.
The developers have put a lot of effort into Elementary OS and therefore in order to encourage people to donate to future development they have defaulted the amount required to download Elementary OS to $10.
You can change this option to $5 if you want to donate but not as much as $10 or indeed if you are feeling generous you can donate $25.
Here is the problem however. If you are unsure as to whether you are going to use Elementary OS long term and you just want to try it out do you really want to donate at this stage. Wouldn't it be better to download it, try it and then after installing it make a donation?
If you want to try Elementary OS for free you can do so by clicking on the "Custom" button and then just enter 0 into the box. You have to click outside of the box for the amount to register and then click on "Download Freya".
If you like Elementary OS you can always come back to the website at a later stage to donate.