Now and then I find some turrets that are surrounded by a red shield. Guns do not seem to do any damage to the shield. How are you meant to destroy these enemies that are being protected by the shield?
You will need to obtain the sword before you can break through the red shields. You get the sword in the first biome. It will be part of the story sort of so you can’t miss it. Once you have it, the game will make you use it and you will know then how it works.