# Building with cards

**Build a scenario** (in **Create**) makes a scenario without writing any file. It has three
parts:

- **Left: cards.** Every block from every router you have, grouped by game. Cards of games that
  aren't ready are greyed out, with the reason.
- **Middle: wiring.** Each block you add becomes a node. What a block **needs** is on its left
  (a world to stand in, collision, input); what it **gives** is on its right. A **Fusion** node
  gives what Fusion provides itself: your keyboard and mouse, the shared collision, steering.
- **Bottom:** whether it can be played, every problem in plain words, how much memory it adds,
  and **Save** / **Play**.

## Make one, step by step

Say you want Minecraft's player walking around VEIN's world.

1. Drag **VEIN → World** into the middle. A scenario needs exactly one World: the place you're in.
2. Drag **Minecraft → Player**. This is who you play as (a **Character** block).
3. Fusion wires them by itself: the Player needs ground to stand on, and VEIN's World gives
   collision. The bottom line says **Ready to play**.
4. Press **Save**, give it a name, then **Play**.

If something's missing, the bottom line says what ("Minecraft's Player needs a World"). To choose
a source by hand, drag from what a block gives to what another needs.

## Settings on a card

Some blocks have settings right on their node: Minecraft's Player has an **Instance** setting that
lists your own launcher instances (your modpacks); a test game's **Walkers** setting picks how many
walk around. The router decides which settings exist; Fusion checks your choice ("12 is more than
8") before Play.

## Change something you have

**Edit** (sandbox scenarios) or **Remix** (Experiences) on an item's page in the Library opens it in the builder
with its cards, wiring and Devices. Save it under a new name to keep the original.

## Make it a game: Experiences

An Experience is a scenario with a title screen, goals and an ending. Add Devices (timers, score
counters, trigger zones) with **F5** while playing, then **Save Devices into the scenario**. An
Experience decides which tools and menus players get, and can lock its Devices. See
[Devices](https://steonmod.com/docs/devices).

## Share it

**Share** on an item's page in the Library saves a scenario as one `.fusion` file, signed with your own key (made
the first time). Send it to a friend: they double-click it, or drop it on Fusion's window, and it
opens in **Content**. Fusion checks the file never carries files from your games.