A “Trust” is where one or more people hold assets or money for the benefit of others. When you make a will you effectively nominate your executors to act as trustees of your wishes for the benefit of the beneficiaries.
The responsibility of the trustees is very serious. If a trustee doesn’t act in the best interests of the beneficiary they can be personally liable. This is known as a “fiduciary duty”. This is why some executors prefer to engage the services of a professional executor.
The wills at Make a Will Online automatically contain trusts for the care of children and looking after life gifts. If you want a more complicated trust to be set up this goes beyond a simple will. You should speak with a traditional solicitor to draft this. An example might be for an income for an adult for as long as they stay in full time education or an income for a spouse or partner until they die or remarry.