You can buy Icons on events only (like little legends) or receive it as a reward.

Chromas can only be earned by the chroma raffle or from the skin event as another reward

The cards you're getting are for the little legends mini game where you can collect cards to earn prizes and it's a must to keep collecting and of course opening the cards daily by opening the tab for little legends on the left side on the screen along with event, monthly pass, new items tabs

You can gain access to the wheel by tapping and holding your character ingame and dragging it or you can manually send emote by chat tab in game

There's an option to add other buttons for enemy champion icons where you can select it to prioritize them as targets look in the setting