You're lvl 19, messing up is part of the experience, just keep playing PVP and you'll improve.
Just remember some mage like ryze are late game, so unless you get lots of farm/kill early, you're not going to be super strong. On the other hand champions like lux , leblanc, ziggs, and etc are mid game terror meaning they're at their peak when they are at mid game. Learn how champions work, if you vrs a frustrating enemy champion mid, analyze their skills and try to think what combos they would use. After the game youtube the champions name and watch how it works.
As for support, try to synergize with your partner, try to think what your partners thinking and if conflict occurs, discuss it out. Communication is key, ping if you want to go ham (to go "all in" or be very aggressive), ping if you see an enemy or friendly jungler come down, and ward ward ward
.
The unfortunate part of MOBA games are that one of the big learning curve is to remember champions and what they do, for new players, expecting to remember over a hundred champions, the skill they use, and their niche; is quite unrealistic.