How to Set your budget in Ads Campaign on Facebook

Facebook allows you to set either a daily budget or a lifetime budget. Here's how they differ from each other:

Daily budget. If you want your ad set to run continuously throughout the day, this is the option you'll want to go for. Using a daily budget means that Facebook will pace your spending per day. Keep in mind that the minimum daily budget for an ad set is $1.00 USD and must be at least 2X your CPC.
Lifetime budget. If you're looking to run your ad for a specified length of time, select lifetime budget. This means Facebook will pace your spend over the time period you set for the ad to run.