Glue, like paste or cement, joins things together. These materials are known as adhesives because they make things adhere, or stick together. Stickiness, however, is not all that it takes.
In order for an adhesive to be practical, it must change from a soft liquid to a hard solid within a short period of time. Sticky substances such as honey, syrup, and chewing gum are not good adhesives because they take too long to harden.
If you were to look at any solid substance under a microscope, you would notice that even those we think of as perfectly smooth actually have bumps and spaces.
Suppose you are making a model that requires you to join two pieces of wood. You would apply the adhesive to one surface and place the other on top.
What the glue does is flow into all the little bumps and spaces of the two surfaces of wood. When it dries and hardens, it grips the two surfaces together.
Glue is made from the skin, bones, and tissues of animals and fish!