Check the season. If it's early spring you can tap your birch. From February until April. Be sure the birch has no leaves yet.
Go out and find yourself a nice juicy full grown birch. Ask it if it's ok if you tap it.
Take a branch which is about 1 or 2 cm thick and hangs down, so the weight of the (full) bottle will not break your branch.
Take your bottle and put the branch in it. Tie the bottle with the wire onto the branch.
Check your bottle frequently, depending on the season it takes a day to get a liter of birchsap.
If you like you can use more bottles on different trees. You can drink it straight from the tree. It tastes like water with a fruity flavor. Enjoy!