You can access Windows Azure as appropriate on the Microsoft platform website. It hosts a calculator that allows you to choose the services you need, calculate their cost and pay for access without leaving this site. The link to the English version of the Online Calculator is below this article, and it is unlikely to be difficult to use if you know how you are going to use Windows Azure. Otherwise, you can get free access to trial the new cloud platform, learn about its capabilities, and decide to use it. The reference to the trial version is placed in the upper right corner of the calculator pages.
To purchase access, you will need to register on Windows Azure and choose one of your plans. You can only pay for the time you connect to Microsoft servers, or pay for semi-annual access at lower rates. You should choose a more cost-effective option based on the planned intensity of your cloud platform usage.