itch.io

It's C#, var is used for convenience, it means that the compiler will figure out the type from the context.

It could be written as this too:

Vector3 cursorPosition = camera.ScreenToWorldPoint(Input.mousePosition);
Vector2 direction = (cursorPosition - transform.position).normalized;

"but I was using only camera.ScreenToWorldPoint(Input.mousePosition);"
I might be wrong, but I think you might not know correctly what does the value of the first line mean.

You need both of this lines, to get the direction which you should shoot from your player.

Here is what it does in detail:

// This is the position of the mouse in pixel coordinates. ie: (1920, 1080)
Vector2 mousePoisiotn = Input.mousePosition;

// This is the position of the mouse in the world, from the camera's point of view.
// This is in meters from the center of the world ie: (1, 4) is 1 meter to the right and 4 meters to up.
Vector3 cursorPosition = camera.ScreenToWorldPoint(mousePosition);

// if this code is running on the player, then
// This is the difference between the player's position, and the world position of the mouse,
// this is how much and in which direction the player should move to reach to mouse's position.
Vector2 difference = cursorPosition - transform.position;

// This is the difference, but it's length is one.
Vector2 direction = difference .normalized;

Normalization could be important, if you shoot a projectile toward the target.
For example:

// This would be going in the right direction, but would be faster, if the difference is bigger.
bulletRigidBody.velocity = difference * speed;

// This would be going in the right direction, and always would be shot with the same speed.
bulletRigidBody.velocity = direction * speed;