For beginners mr price is s good option for watercolor brushes. They sell them in sets.
Keep brushes clean washing them regularly in washing up liquid.
Select a set of watercolor paints. This a set is a great deal. Most sets have a good selection of basic colors you’ll need for transparent watercolor painting. Rarely use the white paint that is included in most cake or tube color sets. It’s opaque. Its use will change your watercolor paintings into gouache paintings. Gouache, or opaque watercolor is a distictly different category and approach to painting.
If you prefer tubes pre-packaged tube sets will also give you a good starter selection of colors for watercolor painting. Start by using brand name “academic” or “student” grade watercolors until you can commit your resources to buying “artist” grade watercolor supplies.
Use any watercolor pad, block, or loose paper with a weight of #140 or higher. The heavier the paper, the less likely you’ll have to deal with the warpage of the damp paper while painting. I recommend larger sheets like this one because you can always cut them in half or quarters for smaller paintings.
Cake and Pan watercolor sets usually have built-in fold out palettes that are useable in varying degrees depending on their size and orientation. For your tube watercolors you can use a flat white dinner plate or buy some inexpensive plastic plates.
Find a glass, or jar, or small bucket to hold fresh, clean water. Use two if possible. One for rinsing your brush between colors, and one for clean water for painting.
Tap water is usually fine. Hard water decreases paint solubility and flow. Overly softened water acts as a wetting agent and increase paint solubility and flow. If you’re concerned, use bottled water.
A few more odds’n’ends will round out your kit. A pencil, a kneaded eraser, some tissues, and an old towel or paper towels, and a couple of large metal clips for holding your watercolor paper to a board. Voila! That’s all you need to start your adventures in watercolor painting