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. 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 allow him to jump in a crowd of enemies in order to land all his other skills. and both damages enemies around Amumu, doing it continually, while doing it in a short but spammable burst. And finally, Amumu's ultimate is , 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. 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. 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 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, , which grants temporarily Mundo additional attack damage as his health drop thanks to his skills or his enemies. And finally, 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.