Any investments made through your PPC campaigns; you’re only paying for each click your ad receives. That is why they’re very effective; you’re only paying every time a user comes to the website by clicking on the ad.
The ad will appear in your browser whenever the user searches for words that you’re interested in promoting.
There are many factors that we can control in PPC campaigns but one of the most important ones is the maximum price you are willing to pay. This parameter determines the maximum value that Google (or any other platform) will charge you as well as define your position against the competition.
There are other factors to consider, but they also depend on the platform you choose. For example Google AdWords takes into account the quality of the advertisement. It is key to optimize texts, the words you use, the call to actions, etc.