Generally, there are two styles of paint containers—pans and tubes. Pans are dried paints that come in a tray with round or square compartments. You must add water to the paint in the pan to obtain a consistency and opacity that works for your painting. Pans are useful if you want to use gouache in field sketching or en plein air painting, or to travel with your paints in an efficient way. You can create your own pans by buying empty trays, filling them up with the colors of your choice, and then letting them dry out.
Tubes contain wet paints. One advantage of paints that come in tubes is that you can load a brush right out of the tube so that you have the most saturated color possible. This works well when you’re using Titanium White for highlights and need the color to be opaque. Tube paints have more versatility in how they can be mixed or applied straight to paper in wet or dry techniques and have a smoother, velvety consistency.
Tube paints that are applied to palettes and then dry out can be reactivated with water just like pan paints. This is one of the advantages of gouache and watercolors: You don’t have to throw them out after each use like acrylics. They stay workable for a long period of time, which is great if you plan to come back to your painting practice only on weekends or after a long delay.