The Billing dashboard is closely tied to the account itself, which is why it is not part of the regular services in the console. Accessing it via the user menu hints at the special access it requires. Generally, you would configure a budget when you first open a new AWS account, so you don't get any surprises in your bill at the end of the month.
If you get access denied messages in the Billing dashboard, it is most likely because you are using an IAM user and IAM access has not been enabled. You must use your root account credentials (such as that you used to create the account), or enable IAM access. IAM access can only be enabled by the root user.
When you first arrive at the billing section, you will see a high-level summary of your usage and expenses. As I performed this example in a new account, there's not much to see at this point. The Month-to-Date Spend by Service graph on the right can be particularly useful to find out what the most popular services you use are. This is a great place to start when trying to reduce or optimize your AWS spending.
We then navigate to the budgets section and create a new budget. Most of the details should be self-explanatory, and obvious for the purposes of budgeting. Your main choice is to decide if you want to alert on usage or costs. Cost budgets work against the dollar (or appropriate billing currency) amount you will be charged. Usage budgets work against a selected unit of usage, for example, instance hours or data transfer for EC2. A usage budget can only track one type of usage unit, so you will need to create multiple budgets to track the various units that you might be charged for. This is one reason why we prefer a cost budget, as it takes into account multiple forms of usage.
Specifying e-mail addresses to alert is the simplest way to send any alerts from the budget. For more advanced use cases, you can specify an SNS topic to receive notifications. An example might be if you wanted to receive budget alerts on your phone via an SMS message, or send the alert to a different system automatically (via HTTP/JSON).
Once finished, you can view all your budgets in the dashboard. You can repeat the process to create multiple budgets. This means you can create budgets for forecast usage and actual usage, as well as different time periods.