Some of these kids are high. You're new, so only focus on learning one champion. Try all the free week champions, and then decide which one you like best. Then spam that champion to oblivion. Eventually, you'll get good at him or her.
You don't need to learn different champions for different roles yet, because in normal blinds, nobody will follow the meta. In normal drafts, the meta is followed, to some extent.
You need 16 champions including the free week champions to play normal drafts. Familiarize yourself with the meta before you get in. Also, learn at least one champion for every role. You can find out who can perform what role by googling around.
It's not possible to put all your mechanics, decision making, etc to the test in normal blinds or bot games, so normal drafts is the only way to practice for ranked.