The executor (sometimes referred to as executrix for females) is responsible for managing the affairs of and settling the estate, including initiating court procedures and filing the deceased's final tax returns.
The trustee acts as the legal owner of trust assets, and is responsible for handling any of the assets held in trust, tax filings for the trust, and distributing the assets according to the terms of the trust.
Both roles involve duties that are legally required. If you don't feel you can carry them out effectively, you may be able to hire a professional to help carry out the duties or step down and allow someone else to assume the tasks.
Each state has different rules and each situation is unique, so you should always consult with an attorney or tax advisor.