Everything you do as a trustee must be done in the beneficiary’s best interests. Exactly what you can and can’t do as a trustee might be set out in detail in the trust agreement. You won’t be able to benefit from the trust yourself (unless the trust agreement says you can).
If the trust is a ‘discretionary trust’, the trustees will have more freedom to make decisions.
How is a trustee appointed?
A trustee is apointed by the settlor or the court and once accepted, can only resign with the approval of the beneficiaries or the court, so it should not be accepted lightly without understanding the responsibilty.