Everybody can use Microsoft Azure for free 3 months (old policy) or $220 to spend on all Azure services (new policy).
However, the free is free, you will realize the free money is gone fast. so you will have to upgrade your Azure subscription. If you do not have a MSDN subscription, what you can choose is mostly Pay As You Go.
Here is an example of upgrading account from free to Pay As You Go:
1: On Azure.com home page, select My Account or Portal, For example we select PORTAL
2: Type an email that you want to sign in for Microsoft Azure:
3: Now you have to login to your Microsoft account with the email which you inputted above:
4: If your free trial expired or no any subscription ordered, you will see the message No subscriptions found. Now please click the SIGN UP FOR WINDOWS AZURE option on left:
5: For my account, we see our FREE TRIAL is no more available since the time is expired, so if I want to continue using Azure, I will have to sign up for a different offer (pay as you go):
6: Now you will see 3 steps to sign with Pay as you Go, Check your cellphone number (when verify, the VoIP phone will not work), input your payment info, the payment only supports Credit card and Debit Card currently, no PayPal supported:
7: After you finished above 3 steps, and click Purchase button, later you will see below screen, which indicates your Pay-As-You-Go subscription is on process:
8: Soon later, you click the highlight text above, you will see your Pay as You Go subscription of Azure is active: