"Turquoise" generally describes a bright, predominantly blue mixture between blue and green. You can, however, mix various shades within the turquoise spectrum: add a glob of white or light-grey paint for a pale and subtle turquoise, or stick to bright blues, greens, and yellows to mix a turquoise that pops. Consider whether you want a brighter or a more subdued hue. The paint medium does not matter much—acrylic, oil, watercolor, etc.—but it will be easier to smoothly mix two paints of the same type. Look for paint online or at an art supply store. Keep your eyes peeled: you may be able to find a pre-mixed turquoise paint that serves your purposes. If you start with turquoise, you can use tiny dollops of blue, green, white, or yellow to minutely tweak the pigment.  If you are new to painting, consider starting with acrylics. Acrylics are a forgiving and easy-to-mix medium, and you can usually buy them in small, cheap squeeze-bottles. If you buy your paint at an art supply store, ask the staff which products will blend well into turquoise. They might be able to suggest specific green and blue hues that are ideal for mixing the shade you want, but do not rely on this. Know which shades you're looking for going in. If you want a paler and more subdued shade of turquoise, you can mix blue and green with white or yellow. The specific hue of white or yellow is largely a matter of preference, so choose something that fits with the mood or style of your vision. For instance, you might choose a warm off-white as a base for turquoise water when painting a tropical beach scene; you might choose a starker, more "artificial" white as the base for painting a cold and distant turquoise planet. Try cyan, cobalt, cerulean, ultramarine – any blue hue that is more greenish than purplish. There are small amounts of other colors hidden within each pigment, which means that each paint shade is predisposed to mix well with a certain other shade. Turquoise is basically a mix of blue and green, so make sure to use a blue that already...

TL;DR in Vietnamese:
Xác định sắc độ màu ngọc lam mong muốn. Mua màu xanh dương và xanh lá. Mua màu trắng và/hoặc màu vàng để tạo sắc độ nhạt hơn. Dùng màu xanh dương hơi ngả sang xanh lá.