You can get to Darkroot Garden from Undead Parish moving towards blacksmith Andrei. Go through his chamber and get to the chamber where you were Titanite Demon (advice on how to kill him can be found in a section about bosses).
Run into a forest and look for a first enemy - these are walking bushes. During the fight keep them at average distance. Monsters can catch you and inflict you a lot of damage. Parry their attacks and counterattack.
After killing the first plant, run forward. You'll get to the junction (the ground is boggy there), where another monster attacks you.
From this place you can go to the right to Darkroot Basin. But leave this location for later.
Go forward, in a direction where your second enemy was coming from.
Once the path turns right, be very careful - a third end will come running to you. Another one lurks nearby behind a small rock. It is hidden in the ground!
A few meters further you'll see a sealed passage (you can by a proper seal at Andrei for 20 thousands souls). Hit the wall left from the magic rune and rumble. You'll reveal a passage and a bonfire. Light it on.
Once you regenerate, continue your walk. Pass by the closed door and choose a path to the left.
You'll reach a fogy passage and another path to the left. There are three ents lurking there. They will jump out the ground when you'll try to pick up an item. You can lure them out by shooting the bushes (these are ents' heads).
Behind fog you'll get to large tract of forest. You'll have to deal there with stone knights lying on the ground. They will stand up when you approach them. During the fight try to avoid their attacks or block them. It is best to circle around them with your shield up. Enemies have one special ability - they may slow you down. So control your stamina if you get hit, to be able to block their blows.
From this large area you can reach the boss Moonlight Butterfly. But it is worth to visit some side paths first. What's interesting, some of them are hidden. Return to the entrance you've used to get here and run along the right wall. Hit the green tree - behind it you'll find one of passages, guarded by frog-ray.
Go down with a side corridor and remove another tree on your way.
Keep on the right wall and use a corridor to go up behind a stone column.
At the top you have to defeat a stone knight. It is worth to kill him, because few meters further you'll find Wolf's Ring.