Character creation in Kids With Bikes is relatively simple.  First, you pick an age group, either child, teen, or adult, which doesn't have a huge in-game effect, but does provide certain bonuses depending on your choice.  Next you pick two positive traits a negative quirk, and finally you pick your stats.

Stats

There are six stats in Kids on Bikes: Grit, Charm, Fight, Flight, Brains, and Brawn.  Each character assigns a single "D&D Die" (either a d4, d6, d8, d10, d12, or d20) to each during creation.  Obviously this means that characters in Kids on Bikes aren't very well-rounded, but instead have very pronounced strengths and weaknesses.

Town Creation

Once character creation is finished, typically as a group, the next step is to create the town that the game is set in.  This is done collaboratively as the GM goes around the table asking players questions about the town.  This process will result in a more fleshed-out initial setting, complete with a number of rumors (the GM can decide which are true and which aren't).

If a player doesn't want to create a character there are also templates (eg. "Bully") to speed things up, as well as example characters.  Also, many games will also feature a "powered character" of some sort (think ET, or Seven from Stranger Things).

Powered Characters

Such characters are created by the GM however, and played collectively by the part: each player is given an aspect of the powered character's personality, and when that aspect becomes the character's focus the corresponding player takes control of them.

As an stat-based system, players roll their appropriate stat die, based on the action they wish to take.  Dice can "explode": if you roll the maximum number on a die you get to re-roll it and add the result.

Success

To determine what number you need to roll to succeed, the game contains a chart, which provides numbers to use based on the action's difficulty.  However, simply rolling above or below the number isn't all that matters: there's also another chart which determines how the action badly/well the action fails/succeeds, based on the difference between the roll and the target number.

Failure

If a character fails at a roll, they gain an Adversity Token as a consolation prize.  These tokens can be spent individually or together, with each one adding +1 to a future roll.  Adversity Tokens can even be used to help another players' roll.

Powered Characters

Powered characters also use a set of tokens, known as PE (Powered Energy) Tokens.  To successfully use a power the player controlling the character rolls 2d4, and spends a number PE tokens (each of which add +1).  Again, the resulting number determines not only whether the power works, but also how much it works.

As a narrative-focused RPG, Kids on Bikes does not have a separate combat system, nor does it have any kind of injury or "hit point" system.  If a character is injured they simply suffer the effects of the injury as decided by the GM.  For instance, if you fail a Fight roll you might just get some bruises and a black eye ... unless you fail badly, in which case the GM may decide you break a leg (in which case the character actually breaks their leg and must recover just as an ordinary person would).

However, that's not to say fights don't happen in the game (after all, Fight is one of the core six statistics) ... it's just that fights are meant to generally resolved quickly as the result of an attribute check, and their outcome is expressed in real-world injuries rather than in a system of hit points.