Typically they are competitive, based on a research proposal. How you use fellowship funds is often at your discretion. Sometimes the sponsoring agency wants a final report of findings, an accounting sheet of how funds were spent, or a professional meeting presentation. The details will be stated when you apply. You can earn a fellowship on top of a graduate assistantship.
Some fellowships are renewable on an annual basis.
If you have worked at a corporation, they may provide partial or full tuition reimbursement for continued education. The policy is one of the benefits many organizations advertise. The company or agency will spell out the requirements for eligibility. Some companies require that you have worked in their organization for a certain length of time before you can get reimbursed. Others may only pay for courses directly related to your career at their company.