Some acrylic mediums can be added in to extend and change the textures and translucency of acrylic paints, others (gesso) can be painted on surfaces to help acrylic paint bind better. Another group of mediums can be used like varnishes on dried surfaces to change the sheen of the coating beneath.
For a miniaturist, acrylic mediums can be an easy way to add texture to all kinds of projects, and in some cases can be used on their own as a stand in for water, jelly, or various sauces for use in dollhouse miniatures.
This gallery shows some of the most common mediums available from art supply stores. Often they are available in small sample sizes or as sample kits, which gives you an opportunity to try them out. Golden Acrylics produce a sampler set of many of the mediums outlined here for under $20 Buy Direct