Experience builds up your level. Your level acts as a multiplier towards voting, so if you're level 5, when you vote you're actually casting 5 x votes. Also, when you login you'll notice you earn minerals based on your level.
Minerals are currently only used when downloading beyond the daily download limit. Everyone gets a huge amount of starting minerals though so you won't have any problem downloading everything you want/need.
Later on, minerals and levels will count towards
other things. I just have to think of more ways they can bring added value to the community without becoming annoying requirements to use features of the website.
Inventory is what is used to hold items, however I think you'll find there are no items added just yet. Getting items is also currently impossible. They, similar to minerals, could be used for future features of the website... and others are simply "collectables". I have no plans at the moment to add any items, so don't worry about that for now. One day it will pop-up in your face, i'm sure

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