Youtube partnerships used to be based on the amount of Subscribers that a user had. However, about 4 years ago Youtube had a large amount of users, so much so that they were getting a few hundred applications for partnerships a day. So now the rule of thumb regarding partnerships is the amount of total upload views you have; or in other words, the total amount of views that you have from all of your uploaded videos combined. With that being said however, getting a partnership is still hard, because they get so many applications it takes anywhere from a few months to a whole year to get around to you (took my application about 6 months), then they need to do a background check to make sure you havent had previous copyright infringements. After that, they determine if your videos will bring in a lot of views, generating revenue for youtube.
If you get accepted, congratulations, you are now a youtube partner. What are the benefits? Well to start off, your uploads have no time restriction, typically videos can only be up to 15 min, well as a partner they can be however long you want them to be. You can completely customize your profile background, add fancy banors to your channel, and youtube promotes your channel more than a usual user. The real prizes however are that youtube automatically protects your original content with a copyright, so you can file a complaint to youtube if someone "steals" your video without permission, and have it removed/the user banned. The other main advantage is that youtube will actively pay you for your videos based on the amount of views you generate, and by allowing Google to place advertisements on your video. Now, if you dont have thousands of views on everyone of your videos, dont sweat, you can still get a partnership regardless, it just means your payments will be lesser than if you attract a larger audience.
The way the payment works is you fist create a Google adsense account, which to put it simply is the Google version of Paypal. Every month Youtube determines your payments based on 2 things: the views and the ads, then sends your monthly payment to your Google adsense account. The catch however, is you dont actually have the money quite yet. Google holds your earnings until you have reached $100 in savings, then you have the option to have a check sent to you, or have it wired to your bank account.
Hope this was informative, and good luck! If you have any further questions regarding getting a partnership, you can send me a message on youtube (username - Cfighter95)