Yeah, the tutorial was made in a hurry (same as the whole game). The diamond-shaped thing with crosses can be placed to catch bullets, which will them fire back when recalled. When collecting bullets, it becomes hazardous to prevent the player from just staying on top of it to avoid bullets.
What was the exact issue with the visuals? I tried to make them easy to follow with the use of colours: blue for the player, red for enemies and hazards and purple for the backgrounds.
Thanks for appreciating the message!