Your campaign budget dictates how often your ads will appear. It is actually calculated on a monthly basis, not a daily one. If you divide the amount that you spend over a 30 day period by 30, you will get your daily budget. But on any given day in that 30 day period, you may spend more or less than your daily budget. They take your daily budget x 30 and divide the suggested budget x 30 by that number. That equals the percent of time that your ads will appear in a month. If they calculate wrong, and they go over your daily budget x 30 in 30 days, than you will get a refund or basically free clicks.
I think that is clear, but it is late on a holiday weekend so forgive me if it is a bit muddled.