Even though copyright protection is automatic at the time of creation/fixation, a work must be registered for a copyright owner to sue against an offender in the event of a violation. Copyright instructions are available at the U.S. Copyright Office website. Electronic filing for a $35 fee is available; filing with alternate paper forms cost $65.
Apart from works made for hire, collaboration often ends in joint authorship. The partnership usually mean that the individuals own the work jointly and be able to execute an owner's rights of the work. Despite the assumption, there should be agreement as to how issues like royalties, revisions, derivative works and permissions should be handled.
You will most like create a body of work in your career, including many in this list:
Additional talents and interests may also produce:
The list goes on, and they all involve Copyright. You will own some of them, sign away some, and share others. Look under the Scholarly Communications tab for Negotiating Publisher Agreements, and under the Employment Considerations tab for Work For Hire information