Acrylics are a type of paint made with synthetic resin as the medium to bind the same pigment as used in oil paints. Acrylics have the advantage of drying faster than oil paints and being water soluble.
Varnish protects finished paintings from dirt and pollution in the atmosphere. The varnish used on paintings is removable so the painting can be cleaned if the varnish itself becomes dirty. Varnish is available in gloss or matt finish. You can mix the two to get your preferred level of gloss. Ensure that your painting is thoroughly dry before you varnish it.
Mediums are added to acrylics to change the paint's consistency (make it thicker so it shows brush marks or thinner for washes) and finish (matt or gloss), slow drying, add texture, and avoid overthinning. If you add too much water to acrylic paint, there will be insufficient binder to hold the pigment together and you end up with uneven paint.
Acrylic paint can be used in thin washes or applied thickly. Use soft sable brushes, or the cheaper synthetic alternatives, for washes where you don't want brush marks to show. Use polyester brushes designed specifically for acrylics for thicker paint. Try brushes with both long and short handles and different head shapes to see which you prefer.
Wooden or plastic palettes can be used for acrylics, but it's difficult to get all the dried paint off. Disposable palettes - pads of paper where you tear off the top sheet and throw it away - solve this problem. If you find the paint dries out too fast, try a palette designed to keep the paint wet - the paint sits on a sheet of wax paper place on top of a damp piece of watercolor paper.
Acrylic paints are available in both student and professional paints. Rather buy quality primary colors and perhaps secondary colors than a whole range of cheap colors. Student colors are more likely to lose their color over time. Some manufacturers make specialty acrylics such as iridescent, fluorescent, and glitter.