I enjoy playing this game but I haven't really learned or went out of my way to know what pp is or how it works/how I get it, or how to increase my rank, stuff like that
You gain pp by setting good scores with good accuracy and high combo on various maps
The pp you're getting from your plays is weighted which basically means that if you make a 50pp play it won't give you 50pp but less depending on how far down is it in your top plays which you can see on your profile page