It seems you are new to Adwords. So welcome to the Community
Billing and daily budget are 2 separate parts of your Adwords account. You have to include the billing details to make your ads running, otherwise they won't run.
Daily Budget is the amount you are willing to spend on daily basis for your Adwords account. More details are available inside the link referred by Neha above.
Is there any specific question you want to ask about billing or daily budget? Please elaborate if you can...