Some traditionalists hate walking poles, complaining that they damage the environment and make too much noise. But a growing number of converts and devotees now rarely hike without them.
Used correctly, poles assist with balance and lateral stability (helpful when crossing streams or rocky terrain and traversing steep hillsides), and lessen the strain on knees on descents (a kindness to joints of all ages). Poles also make good depth-finders to test water or mud on walking tracks!
And while some hikers pack them away on the flat, I have found that using poles helps me maintain rhythm when striding out. The arm exercise also prevents the fat fingers I otherwise suffer.
One or two poles? It’s a personal thing you will work out only by experimenting.
There is lots of on-line written and video information but to begin, adjust the pole length so your forearms are at roughly 90 degrees to your body. Now put your hand through the strap from below so it rests on the strap when you release the handle; this facilitates easy swapping between the standard grip and cupping your hand over the top for descents.
Most walking poles now come with rubber caps over their metal tips. These give a good grip while muffling the sound and limiting rock scratching and hole punching; but ensure they don’t come off and get left behind in fragile environments.