If you are going to invest money in PPC, so by using programs including Google AdWords, you will be able to put your links all over the net, reaching out to more markets and spreading the word about your site, generating traffic for your business and improving chances to make money as well. For clicks made on your ads, you will be paying some amounts of money and you can manage your spending by setting budget limits for campaigns.
On the other hand, there is an opportunity to earn revenue from the net through publishing ads on your website. The Google AdSense can be named in here and thousands of websites can be found which have been monetized via that program. By placing ads on your site, you will be able to earn commissions paid to your account, originated from clicks made on the ads published on your site and can have a monthly income.