Blocks snap into each other to define the program that will run. Blocks can be event (buttons, shake, ...) or need to be snapped into an event to run. The on-start event runs first.
for (let i = 0;i<5;++i) {}
if (true){}
let x = 0;
Math.randomRange(0,5);
"".compare("");
[0].push(0);