When I was starting out the game I didn't use Clarity, but I didn't really have any idea what I was doing and it was mostly just my boyfriend telling me what spells to take. However, at your level I think Clarity is a decent spell because you've not fully learned the ropes of mana management just yet, nor are you going to be killing minions early enough to get mana regeneration in your build quickly.
Clarity isn't picked once you have played the game for longer because mana management becomes a lot easier for a few reasons - people pick up mana masteries (Expanded Mind gives you an extra 75 mana I believe?) and further in the utility tree, Meditation gives you a powerful amount of mana regeneration when you run low (though you rarely get masteries like this except on supports). Mana regen glyphs are also quite good to help you avoid running out of mana (personally I use them on mages because I'm still trying to improve my mana management).
I just took a brief look at your matches and from what I gather you don't build your mana item until quite late, which you should try to not do. Typically your mana item should be the first one you complete, allowing you to spam your spells (and make Clarity unnecessary!) quite a bit earlier in the game.
tl;dr Clarity is a great idea to take at your level but as you advance (not necessarily soon, but eventually) you should try to rely less on it and get better at using your mana. A mixture of masteries, runes, completing mana items early and becoming more clever about when and when not to use your spells means Clarity ends up not really being essential.
p.s. You should start buying boots :) They're really boring items but they're very powerful, you shouldn't underestimate the power of your champion moving quicker! And they have a lot of powerful effects attached when you upgrade them too, for example Sorcerer's Shoes and Ionian Boots of Lucidity are very strong on Morgana :)
p.p.s. Good luck learning League and I hope you have a lot of fun with it :D