It's simplicity itself! Harvest clean leaves, rinse them (dust, bird poop, etc) and (if you want) dry them for storage. No reason to not use fresh for tea, though, in season. Chop up enough leaf to make about a tablespoon of chopped plant material, and put in a tea ball. Add boiling water and steep. Add honey to taste (it's bitter)
OR, dig the roots, scrub and dry. (if the root is thick, split it- like cutting a carrot in half lengthwise). Chop pieces of root- about 1/4-1/2" thick. Put in a stainless steel or glass pot (never use aluminum for preparing medicine!), cover with water, put a lid on the pot and simmer for 10-15 minutes. This makes a "decoction"- and is necessary to get the medicine out of the root.
You might want to look for the book called Handmade Medicines, by Christopher Hobbs. It's out of print, and for awhile the prices on Amazon were insane- up to $100 for a used copy (and it's a small book!). However, supplies seem to have loosened up (funny how supply and demand works!) and the price was down to reasonable levels the last I looked.
It's a great basic resource, and even has alcohol/water ratios for many herbs... not all of them should be tinctured at 100 proof, or 160 proof....
Summerthyme