Skins are often a way for a video game developer to let their players customize and make their own version of the characters they will be playing for hours. This is true in many games, especially online multiplayer games like Back 4 Blood. Here is how to unlock skins and equip them in the cooperative shooter.
To unlock skins in Back 4 Blood, you need to gather and spend Supply Points at the Supply Lines section in Fort Hope (the hub area). You can find Supply Lines by finding the woman sitting at the picnic table or bringing up the menu.
When in Supply Lines, you have to work on a track and unlock items in order to get to the next thing. When you complete a line, you will open a new one.
Very early in your Back 4 Blood career, most of these unlocks will be for cards and sometimes personalization items in your profile. Keep working through the Supply Lines, and eventually, you will come across one for new character cosmetics.
When you have those new items, make your way to the tent in the middle of New Hope or open the Cleaners section in the menu. You will get a breakdown of all the items you have for each character and can pick and choose how they will look when you play as them.