Choices...choices! Watercolor paints are sold in tubes and pans. I prefer tubes as you can mix up larger quantities and strong colors more easily.
Tubes are make in a standard size, which may look small when compared to tubes of oil or acrylic paints, but actually last a very long time. Tube paints are available in two types: student or artist. Student paints are less expensive because they contain less pure pigment. Artist watercolor paints can sometimes cost twice as much as student paints. Although many artists suggest that one never purchase student paints, I have never been disappointed. For someone just starting out, I would recommend trying student paints in a good name brand. It can be quite costly to buy all artist paints especially if you don't know that you will like watercolor painting. If you do enjoy watercolor painting and plan to continue, replace your student paints with artist paints when you run out of a specific color. Then you can decide for yourself if the additional cost for artist paints is worth it to you.