With Google Ads (previously known as Google AdWords) you only pay when someone clicks your ad. All your spendings on advertisement go directly to Google. Your costs are made up by your max. CPC, your daily budget and eventually the number of people clicking your ads. On some days you might end up spending more than your daily budget because Google see a potential for attracting more traffic to your site. These days are then balanced by days where your website or online shop receives less traffic. No matter what, you'll never end up spending more than your monthly charging limit, which is your daily budget multiplied by the average number of days in a month (30,4).
To manage your budget and other settings of your Cobiro account, you can always log in to your Cobiro Dashboard.