I need to know about computers?

Hey I'm 13 so this might need to be dumbed down a little, but I'm a PC gamer and currently have the HP ENVY Phoenix 810-460 (heres a link http://store.hp.com/us/en/pdp/desktops/hp-envy-phoenix-desktop---810-460#!&TabName=specs) and the monitor is here http://store.hp.com/us/en/pdp/accessories-88342--1/hp-envy-24-238-inch-diagonal-ips-monitor-with-beats-audio. This was my first major gaming PC. (I had a laptop before but it was horrible) I will probably just keep updating it as time goes on, but I basically just need to know about the parts of a computer. What I don't understand is what makes one motherboard better than another, how the same amount of gigabytes/terrabytes on one harddrive might be worse or better than the same amount on a different type, basically I dont understand what a video card is, et cetera. Can someone basically just give me a somewhat dumbed down lesson of what everything does and does not do?

P.S. On it I play all games from Call of duty to Garry's Mod to minecraft to some retro.

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