A good idea would be (like they made in the Dota 2 Wiki) to write, right under the stats and just above the abilities of all champs, a short-medium introduction that says, for example, the playstyle, main role(s), synergy between skills...

Here an example to be clearer (I'm not good at this, so feel free to correct me) :

Amumu is a melee tank initiator champion, who rely on being in the center of a battle to be truly effective. Cursed Touch Cursed Touch gives Amumu's autoattacks a quite powerful debuff that increases the magic damage dealt not only by him, but also by his teammates. Amumu's signature Bandage Toss Bandage Toss allow him to jump in a crowd of enemies in order to land all his other skills. Despair Despair and Tantrum Tantrum both damages enemies around Amumu, Despair Despair doing it continually, while Tantrum Tantrum doing it in a short but spammable burst. And finally, Amumu's ultimate is Curse of the Sad Mummy Curse of the Sad Mummy, which not only damage nearby enemies, but also disable both movement and autoattacks, both effects covering an huge area.

EDIT : here is another example, a little differently :

Dr. Mundo is a melee manaless champion, who use his health to cast his spells. Adrenaline Rush Adrenaline Rush gives Mundo a boost to his health regeneration based on his health, allowing him to get some sustain by building health to mitigate his costs. Infected Cleaver Infected Cleaver is a spammable skill that not only come with a helpful slow, but also damage that scales with the target's current health, making it good for both chasing, harassing and initiating Burning Agony Burning Agony is a toggle that drains Mundo's health in order to damage all nearby enemies over time while resisting crowd control, making it a perfect synergy with his next ability, Masochism Masochism, which grants temporarily Mundo additional attack damage as his health drop thanks to his skills or his enemies. And finally, Sadism Sadism is Mundo's ultimate, on a quite short cooldown for an ultimate, it allow him to regenerate a large portion of his health as well as gaining a burst in movement speed.