are all the champions I recommend new players master if they want to learn Top Lane. Poppy teaches positioning and trading. Maokai teaches the value of vision and the role of Top Lane after the laning phase is over. Renekton teaches trading and how to play aggressively. Shen teaches map awareness, tactical awareness (as in, being able to predict how to interact with the enemy team by properly reacting offensively or defensively to their actions), and improves reaction time.
Once you have mastered all of these champions, you can usually go on to play whoever you want. While you will of course need to learn every champion you play, these champions will allow you to master gameplay mechanics that span across multiple champions.
I would also recommend playing
to learn how to deal with ranged threats when you have a lack of range (sometimes it's best to just stand there and look threatening) and
to learn how to manipulate/freeze the wave and help a little with learning how to last hit.
While it is important to play the meta or just be really damn good at one champion if you wish to climb the ladder, I cannot stress how important it is to learn the inner pieces of League before jumping in, picking the FotM, and trying to blast someone. You will likely win many matches, but learning the various ways that LoL works will in the end allow you to win many games you would have lost.