A trust exists when one person (or persons, or organisations) holds particular property for the benefit of ascertainable people or purposes, in a manner permitted by the law. The trustees are the legal owners of the trust property (or trust corpus), but they are obliged to hold the property for the benefit of one or more individuals or organisations (the beneficiary), usually specified by the settlor. The trustees owe a fiduciary duty to the beneficiaries, who are the "beneficial" owners of the trust property. The idea came into English law at the time of the crusades, and has been continuously elaborated in the courts ever since until it is a maze of precedent and a minefield of difficulty.
The general law of trusts requires that the trust property must be certain, the identity of the trustee must be certain, and the beneficiary of the trust must be certain and of a kind permitted by the law. The types of trusts that are permitted by the law are trusts for persons, or for purposes that are charitable (in the most narrow of legal senses), or for a very limited set of non-charitable purposes (for the benefit of animals and monuments, for example).
You can set up a trust, or a trust may be presumed from your situation, or may be forced on you by law. Its activities may have tax implications, or may not. A trust can be expressed in writing, or it can be implied. There are no particular forms that must be used to create a trust, and there are thus no simple procedures to follow.
The law of trusts is fanatically complicated. It is impossible to compress it into a few lines, or a few pages, and still have it mean anything to the uninitiated. If you want to set up a trust, or if you want to know what a trust binds you to do, or if you want to know the tax implications of a trust, you have really no choice but to seek out a lawyer.