DBA for partnership
From your question I understand that you would like to create what is called a "General Partnership", which is an unincorporated non-limited liability entity. Typically you would need to draft a Partnership Agreement that would govern the relationship between yourself and your partner, and then register a DBA for this partnership. Depending on your state, this would be done with your state and/or county, or your city/town.
We can help you register the DBA with the appropriate authorities, you are welcome to visit our Doing Business As page here.