I am starting up an online boutique for clothing and accessories and am living in manhattan. Is there any paper work required, also i am 16

As a threshold matter, you are not legally capable of entering into binding contracts relating to this business, nor can you address the other key issues on your own. When you say you are "working with" an adult, that's fine, but it's not sufficient. Since your business is apparently operating as a proprietorship, you will need to file an assumed name certificate with the County Clerk, obtain sales tax authorization from the NYS Department of Taxation and Finance, and, if necessary, obtain an Employer Identification Number from the IRS.