You can use any craft, water based, acrylic paint. Same thing tole painters and decorative artist use. Patio Paint, Delta Creamcoat, Apple Barrel, Folk Art, etc./. They commonly come in 2oz size plastic squeeze bottles. I get the larger 4 or 8 oz bottles for commonly used colors like black and white. Common colors like white, black, green, blue, red, gold, yellow, burnt sienna, and brown will get you started
You can use a variety of brands and type of sealers. Make sure its the non-yellowing type. I like, and currently only use the Delta Ceramcoat as show above, back row center. I use the matte for my realistic animals and gloss finish on my other rocks. It's just a personal preference decision. I like to brush my sealer on rather than using the spray. You have to take the spray outside and find a spot that you don't mind getting spray on, or lay newspapers down to protect the area. If it's a windy day, have fun! The rock "smells" for a while when you bring it back in till its good and dry. Try them both and see which one you prefer. I use Elmers Wood Filler to patch any small holes or to make the bottom of the rock a little more level when I have a "tippy" rock. Get wood filler for outside use. Apply it in thin layers, wetting it to smooth it out. Wait till dry to apply another thin layer if you need to.
There are a bunch of rock painting books published, but they are hard to find in stores. Sometimes the craft stores or bookstores carry them, but only the newer ones. To find the older ones and even newer ones often, you will have to buy them online.
You can see what's available and buy them by going to the Books / Rock Painting & More section on my web site which will take you to links on Amazon.com where you can buy them new and used.