[ZAMIRZ]

Where are you riding that you need to do these tricks? I've been mountain biking for 20 years and haven't come across any obstacle where I needed to trackstand or manual like a trials rider. If you want to do it just for fun, you can practice doing a manual in a grass field and fall on your ass a bunch until you get it. Trackstanding is also easy to learn without hurting yourself, do it in the same grassy field or just hop off if you're about to tip over onto asphalt.

If you want to descend quicker and more smoothly, there are a couple things you can do. Break the descent down into sections and focus on taking better lines, looking farther downhill helps. Start shifting your weight around more, fore/aft movement makes a huge difference. Finally, you're probably not carrying enough front brake. Keep your weight back and low and try hitting that front brake harder and later. If you're losing control, experiment with shifting your weight by extending your arms or bending more at the elbow.