Deism is the belief that there is some form of supernatural being or force that was involved in creating either humans or at least part of the physical world. Deists tend to have less confidence as to how human-like their god might be, and don’t necessarily include a belief in an afterlife. Deists are convinced a god or similar supernatural force of some type exists.
Agnosticism is the belief that it is currently unknown whether there are or were intervening supernatural beings or forces, and postulate that we will probably live out our lives on planet earth without being able to verify whether such beings exist or not. Agnostics are neither convinced a god or similar supernatural force of some type exists or that they don’t exist.
Deists and agnostics are often in agreement in disbelieving in the existence of specific religious versions of gods such as the Tao, Yahweh, Allah, Brahmin or other such beings. They also are often in agreement in being unconvinced or even entirely disbelieving that any supernatural activity has taken place here on planet earth.
The main difference usually involves how they define or view the idea of the eternal something. Deists are convinced that some type of supernatural being or force must have always existed that either created physical existence or always existed alongside it.
Agnostics are not convinced of this, but also not convinced that physical existence itself or a natural world could have always existed without something that might be called supernatural, either in the form of a being or force of some type. To be an agnostic essentially requires believing that a supernatural explanation for an eternally existing physical world is at least plausible.