You may not own the trust - you likely became a trustee and a beneficiary of the trust - but the distribution from the trust may be partially taxable.
It is not clear if your inherited cash or mutual fund shares - inheritance is not taxable - so whatever you inherited from your mother is not included into your income tax return.
Any income received in that account before your mother died - interest, dividends, etc - should be reported on her final return.
However if you inherited mutual fund account - and sell shares - you may recognize capital gain - if any case - you meed to report the sale transaction on the schedule D.
Your gain = (selling price) - (basis), where the basis for inherited property is a fair market value on the day your mother died.
You need to report the sale transaction and determine the basis - if you do not report - the IRS would assume the gross sale amount is your income.
If you sold shortly after your mother's death - it is likely - no or very small gain.
If you inherited tax deferred mutual fund account - like IRA, 401k, etc - it is taxable when you take distribution. You may spread distribution over several years to reduce tax pressure.