If you mean to ask how to you start earning by uploading videos on YouTube then you need to follow these 3 simple steps.
1. Enable monetization in your YouTube account and join the YouTube partner program. This will make sure that you earn money to play ads before your videos.
2. Second you need to have an AdSense account where you get paid for playing those ads.
3. After you have enabled monetization and set up an AdSense account you can turn on ads for eligible videos. Make sure that your videos are eligible for playing the ads before them.
If you follow these steps along with all the onscreen steps while setting up your account you are good to go.