Liner brushes are great for doing lettering work, line work, and detail work. The length of the size will inform you how much paint that liner holds. The smaller the number the smaller the length and width of the liner will be which in turn means that it will hold less paint.
Synthetic Sable Paint Brushes are the perfect go-to for any level of artist. Synthetic brushes are perfect for watercolor and gouache because they last longer than natural hair brushes and the bristles don't fall out while painting.
Proper care tips: Make sure to clean your brushes well after each use (with water) and only use these brushes with watercolor and gouache.