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To become a YouTube Partner, you need to enable your YouTube account and successfully monetize at least one of your videos.
YouTube's guidelines for successful monetization are here, but in a nutshell, your best bet is to create original content while owning all the rights to commercially use all the visuals and audio in your video.
YouTube Partner program is currently available to everyone in these countries: Argentina, Australia, Brazil, Canada, Colombia, Czech Republic, France, Germany, Ireland, Israel, Japan, Mexico, Netherlands, New Zealand, Poland, South Africa, Spain, Sweden, United Kingdom and the United States.