If I create a comic art work for t-shirt sticker or wall stickers, do I need to take copyright approval from the main company?

When you create an original work of art and fix it in a permanent medium, copyright protection is immediately attached to the work. However, if that design includes work created by another person or company (work that is either copyrighted or trademarked), you will need prior written approval to copy that work and then to distribute it as part of your design. I'm not sure what you mean by "free to use policy."